The Day of the Troll
 Siblings Karl and Katy are in an old, scary forest - Karl winding his sister up. We learn that Katy is a former "medical type", and that the two are involved in experiments - experiments that are being ruined by something. They find a geo-sensor, a stubby plastic pole, which Katy examines. It's gone offline, even though Katy checked it two hours previously. We learn the two grew up in cities, and joined a project that involved them coming to this country, unlived-in for fifty years. Karl finds an old bridge which Katy recognises. On the bank is a line of smooth earth, as though something was dragged along the ground, all the way to the bridge. Karl insists on taking a look. Katy finds that she has her own torch. She follows her brother, standing in the dried-up river. The bridge is an old railway one crossing the former river. She spots a shape under an arch, assuming it to be Karl - and then realises it's not. She runs away, colliding with someone, who grabs her. He introduces himself as the Doctor. As the sun comes up, the Doctor examines the soil. It's not a desert, but it's so dry - he assumes a drought at first, but then it starts to rain. Katy moans, having done nothing but stare all night. The Doctor examines her practical clothing, and the logo on her cap which reads "The Grange". He takes the cap and puts it on. The Doctor leads Katy away, seeing the land divided into fields, sensors in each one. He recognises it as England. We learn that Karl is an entrepreneur, funding the Grange project to work in the abandoned southern Britain to grow crops and conduct agricultural experiments. Petra Lancaster is visited by Dr Timothy Hill, a botanist who works for the project. Petra reveals their campaign for money has not as successful as necessary. They see the Doctor approach, and Petra storms out. The Doctor introduces himself, and they turn their attention to Katy - who's in a state of shock. The Doctor uses the psychic paper to convince Petra to let him lead an investigation, although she remains suspicious. The base of operations is a former country house. Katy is taken to the infirmary and examined - confirming she's in shock. Charlie Bannon, the bullish Grange mechanic, arrives with news - Karl and Katy's 4x4 is missing. We also meet Vanessa, a posh biology student. Katy speaks suddenly - she's terrified, and mentions something under the bridge. Petra watches Food Minister Hamilton Bryant on her monitor, talking from Madrid - assuring her not to worry about Karl and Katy. He threatens her not to let the world know about this by sending anyone to help them - he has a financial interest in the Grange succeeding. Petra asks about the Doctor - Bryant is clueless, but suggests she take advantage of the extra help. Charlie and the Doctor drive a 4x4 towards the bridge. The Doctor asks for details on the Grange. Charlie explains that humans used a process dubbed Global Cooling, refreezing glaciers. The ground left behind was poisonous, and food became incredibly value, leading to violence. Karl Baring started work on growing new crops, but so far, hasn't succeeded - running out of money, depending on charity. They arrive at the bridge as Charlie explains that no-one cares about the project anymore - and without Karl, they don't stand a chance. The Doctor runs for the bank and starts to investigate. Charlie follows with a shotgun. The Doctor points out the mud is undisturbed - no signs of a struggle. Someone's covered the tracks. He questions why anyone would wait until the middle of the night to kidnap Karl Baring. The Doctor dashes off. Charlie notices something caught in the ivy on the bridge. When the Doctor returns, he finds Charlie's shotgun abandoned. He's still searching for Charlie two hours later, when Petra and Vanessa arrive. Hamilton Bryant once again turns down Petra's request for help. In the common room, Petra reveals that no-one has moved in or out of Britain since a supply drop six weeks previously. Petra reveals that no help is coming. Campbell, South African overseer of the field operatives, points out Karl and Charlie only went missing after the Doctor turned up. Others, including red-haired native volunteer Sanders, disagree. However, Petra suggests it could be one of their own number. The Doctor points something out - roots on the floor, vegetable matter walked through the Grange. Tim doesn't recognise it as their own, and the Doctor tells him to analyse it. At night, the Doctor visits Katy, ignoring Petra's protests. He wants to know what she saw. Vanessa's present, taking care of her. Katy's being kept in the former Baring family nursery. All she'll say is "not under the bridge". Sanders contacts Petra to tell her the relay link's down - they can't contact Madrid. Either they were shut off in Madrid, or the local relays have been sabotaged. Recognising Katy's fear as childhood fear, the Doctor guesses whatever's here has been here all along, and that it's something from a childhood story. Vanessa spots a book called "Not Under the Bridge", which the Doctor takes and reads. He then leaves immediately. Meanwhile, Tim examines the plant matter. The Doctor arrives, and Tim explains the plant's genotype has been altered. The Doctor suspected it's been reprogrammed to move around the house - to use plants as a vehicle. The Doctor leaves as Tim discovers something else that's strange about the sample. The Doctor gathers everyone to the common room, with a screen set up for Katy. The Doctor proceeds to tell the story of Not Under the Bridge. In the story, a troll lives under the bridge, looking like it's made of twigs and rope. In years where not much corn grew, the troll woke up and found a maiden to eat. The Doctor claims a troll really does live under the bridge. Behind the Doctor, something is crawling into the room - a beast made of twigs, the size of a baby. It crawls along the ceiling. Campbell tries to jab it down with a broom handle, but the creature grabs it and starts to move down. Campbell throws it away, and it lands in Vanessa's hair. The Doctor grabs the creature, pulling it away. He places it on the table as it disintegrates into roots and berries. Petra sees something on the computer screen - something in Katy's room. The monitor goes dead as the Doctor realises the small beast was a distraction. Petra instructs everyone to lock up the windows and doors. She heads upstairs, meeting the Doctor, who’s listening outside Katy's room. He opens the door. A small man is bent over Katy's bed, covered in roots. The Doctor closes the door again, and they hear the creature hammering the door. From the room, the creature room asks them to "come under the bridge". They hear the creature escape through the window, and enter the room. The Doctor climbs over the edge of the balcony, jumping his way down, and running after the beast. Petra looks down, and sees the creature running towards the gate, carrying something like a blanket. She realises Katy's been taken. We learn that the creature escaped through the gate. The Doctor follows slowly, knowing the destination. On route, he trips over Katy Baring in a bedspread. She seems happy - she believes Karl came for her. A 4x4 approaches them from the Grange - Petra, Campbell and Sanders. Sanders is told to carry Katy back to the Grange, and the Doctor joins Petra and Campbell to head for the bridge. Near the bank, they stop and get out to walk. At the dry riverbed, Petra sees something moving in the darkness. Campbell raises a shotgun, and fires into the darkness - but it isn't the troll. Suddenly, Campbell is grabbed by the troll. The Doctor manages to grab it, and recognises its face - it's Karl Baring. They struggle, the Doctor is knocked down, and the troll attacks. Petra fights the troll off with a branch, releasing the Doctor. He tries to grab the creature with a parka, but underfoot, the ground forms tentacles which attempt to drag them under. Petra helps the Doctor trap the troll with her own coat, and the limbs disintegrate. They spot a helicopter overhead, which lands nearby. Lieutenant Chavez of the Eurozone Reaction Team, a neat young man, exits - the people at the Grange had sent him after Petra. They head back in the helicopter, taking the troll with them. Hamilton Bryant is on board. He intends to burn out the area - the helicopter fires napalm and explosives into the forest. In the common room, the Doctor and Chavez unwrap the troll. The Doctor attaches it to a robotic medical unit. Hamilton clashes with the Doctor, so Petra leads him out of the room. Tim recognises the troll as Karl. The following morning, the troll seems uncomfortable in the light. The Doctor tries talking to the troll - he knows it's being animated by some life force. He asks what Karl Baring would call that life force, and the troll replies, "Spheriosis" - that which feeds from beneath. We learn the Spheriosis landed long ago, and fed with their roots until there were no nutrients left. They had to change, to absorb oxygen and nitrogen. The troll passes out from the effort of speaking. Hamilton Bryant is with Petra in her office. She realises it was him who shut off the relay links - and Bryant reveals he has no intention of leaving without Karl Baring. The Doctor gathers everyone again. He reveals that the Spheriosis landed billions of years ago, growing enormous over eons, closer to the surface. The Doctor suggests they all leave, but Bryant refuses. Petra asks about Charlie and Campbell - and the Doctor explains they've been eaten by the Spheriosis. The troll sits up, passing through the straps which were keeping it trapped as though made of mud. It once again asks everyone to "come under the bridge", and dies, crumbling in front of them. This time, Hamilton Bryant gathers everyone. He wants Petra and Katy on a helicopter in fifteen minutes, and orders the Doctor's arrest. He instructs Tim to perform an autopsy on the troll. Everyone else is instructed to stay behind in the Grange. Chavez locks the Doctor in a dark cellar. Upstairs, Bryant's lackey Stephenson sedates Katy, ready to be taken to the bridge. Two troopers bring Tim Hill into the room - Sanders intends to walk to the coast, taking an emergency flare. Petra stands up to Bryant, telling him not to take Katy. He orders Chavez to shoot her. After a face-off, Petra stands down, and Bryant tells Chavez to put his gun away. The Doctor realises that the Spheriosis is under the house – it’s enormous. Above, he hears the helicopter being boarded. Airborne in the helicopter, Katy wakes up. Bryant tells her they’re going to see Karl. Petra insists that Karl’s dead, his body being used by something. Nonetheless, the helicopter reaches the scorched riverbank. Explosives have damaged the soil, but the bridge is still intact. They leave the helicopter, and spot a flare in the distance – Sanders, proving that the Spheriosis reaches far away. Katy starts approaching the bridge, calling for Karl. Suddenly, Petra breaks away, and runs for Katy. Chavez shoots her, and she falls down the bank. In the cellar, the Doctor hears the Spheriosis under the ground again. He jumps for the stairs, and a trunk of roots breaks through the ground into the cellar. The Doctor calls for help, attracting the trunk’s attention. It shoots at the Doctor, just as the door is unlocked. The Doctor escapes, and the door is closed by Vanessa. The Doctor blocks the door with a stack of chairs, and they run. Vanessa explains she heard sounds coming from the lab, and the Doctor guesses it had been Tim. They reach the lab, and enter. Tim is nowhere to be seen – only the remains of the troll on the table. They hear something on the floor, and find Tim entwined in roots, being pulled down a hole. The Doctor knows it’s too late. More roots crash through the ground. The Doctor realises that Karl Baring is still within the creature somehow. Later, the Doctor takes a car from the Grange. He explains to Vanessa that the troll was warning Katy away. Karl had enough influence to save her, but not to save her if she came under the bridge. He tells Vanessa to take a car to the coast and organise for Britain to be left alone, letting the Spheriosis starve. Katy runs to Petra, who’s still alive. Men gather at the top of the bank – Petra tells Katy to run. Bryant instructs Chavez to have Katy taken under the bridge before they evacuate. Corporal Stamper and Doctor Stephenson are sent to get her. Chavez follows Bryant down the bank. Katy is led over the bridge. Bryant slaps her, thinking there’s nothing under the bridge, and that Katy’s trying to trick him. As they move, Stamper stops, looking at the ground. Long, thin white arms burst from the ground, pulling Stamper underground without a trace. Stephenson runs, but is swarmed by roots, which pull him into the ground. Chavez shoves Bryant out of the way and escapes, leaving Bryant to the creatures. Bryant shoots at them with his pistol – and realises Katy is being left alone. He grabs her, while up ahead, Chavez shoots himself having been grabbed by the creatures. A car arrives on the scene, driven by the Doctor. Bryant and Katy climb aboard, and they drive away as a single gigantic tentacle bursts from the ground. He asks about Petra, and Katy tells him she was shot by Bryant’s crew. Behind them, the tentacle has stopped chasing them. It grows – as tall as a block of flats, and beyond. The Doctor realises Karl’s forcing the Spheriosis to waste its energy, to save Katy. The three of them exit the car. The ground is shaking, but the Doctor knows the power struggle is evenly balanced. A creature breaks through the ground – the troll. Behind them, Bryant takes the car and drives away. Around them, more arms break through the ground – more trolls. The Doctor guesses the way to keep Karl fighting is to put Katy in maximum danger – to take her under the bridge. Bryant speeds away, avoiding the creatures. He drives for the bank, but crashes, activating the airbag and stalling the engine. A troll attacks the car as Bryant tries to get it going again – and then a second troll, followed by a whole pack of them. Roots break into the car, spreading and growing. They fill the car as the trolls watch. Under the bridge, the Doctor sees the roots approaching, and tells Katy to talk to Karl. She tries, and attracts the attention of a troll. She continues to shout for her brother, causing the troll to double up in pain. The Doctor hauls the troll under the bridge, and throws it at Katy. She recognises Karl as he sighs, and the entire creature disintegrates – including the tentacles outside. The Doctor digs his way out of the ground, pulling Katy back after him. She tells her Karl managed to kill the creature. Metres from the bridge, they spot a half-buried Petra – still alive. Katy attends to her. The transport helicopter arrives a moment later – Petra will be saved. The Doctor announces he’s leaving. The farm will flourish now without the Spheriosis draining its nutrients. Katy and Petra will be fine.