Elfangor's Secret
K. A. Applegate
 The former Visser Four inadvertently discovers the Time Matrix and uses it to rewrite history to make the Yeerk domination of Earth much easier - America is now a technologically inept, genocidal empire; Jake is a neo-Nazi who demands to be called "Supreme Leader" by the other Animorphs, and Rachel is in a re-education camp to be "taught her place", her role on the team now being filled by Melissa Chapman. None of the Animorphs are aware of the change, as this is, to their minds, what life has always been like, Visser Four having changed events before their births. The Ellimist and Crayak have formed a temporary truce in order to stop Visser Four, and they send the Drode to offer the Animorphs, having restored their true memories and line-up, a Hobson's choice; they can refuse the opportunity to track down Visser Four, and the timeline remains as it is, or they can defeat Visser Four and return the timeline to how it originally was... for the price of one of their lives. The Animorphs of course have no choice but to accept, and set out to stop Visser Four's rewrite of time. The Animorphs pass through many historical events, including the Battle of Agincourt, Washington's crossing of the Delaware (in which, as Marco and Cassie predicted and feared due to his previous actions against Crayak, Jake is killed in the crossfire), the battle of Trafalgar (in which Rachel, Marco, and Ax are also "killed", but not really due to the only required life, Jake's, being taken), and finally Princeton University a short time after 1932. It turns out that the American colonists lost to Britain and the Hessians, and France won the battle of Trafalgar, leading to the U.S. and England having to make peace with Napoleon Bonaparte. The United States - or rather, whatever the country is called now - is still under British control. However, Visser Four had made a mistake. Although originally planning to kill Albert Einstein at Princeton, his own meddling in the past had changed the future so that Einstein was not at Princeton at this time (still in Germany). Furthermore, Cassie and Tobias make the discovery that Rachel, Marco and Ax have been resurrected, and thus the remaining five Animorphs realize that the Ellimist's conditions allowed that only one Animorph could be killed; with Jake's death, the rest of the Animorphs are essentially immortal, albeit just for the duration of their mission. Visser Four begins to rapidly leap through time and space in order to shake the Animorphs off, but when he is unable to lose them, he directs the Time Matrix to the Normandy Landing. After navigating through the time-altered battle (including an Adolf Hitler who is a harmless jeep driver and the French and Germans on the same side), the Animorphs close in on Visser Four, whose host body (John Berryman) has been fatally injured. Visser Four abandons John's body, and Marco kills the Yeerk. Cassie, much to her chagrin, asks John where and when his parents met, and the Animorphs direct the Time Matrix to San Francisco in 1967 to prevent John's parents from ever having met. But when they get there, they start to debate the morality of their intended actions; maybe history would be better somehow if they didn't cut off his life. However, they accidentally distract his mother, so she never meets his father and they never have to make the choice. With John never being born, he was never infested by Visser Four, who in turn never found the Time Matrix, and the events of this story never actually took place; Jake returns to life, as the Animorphs were never actually at the Delaware crossing. Despite the reset, the group remembers everything, even after they go home, due to Drode having buffered their memories and personalities.