 The explosion is actually half of the Downside, which was destroyed, and sealed up as a result, in a plan by Talon to keep the Topsiders out.The plan works, and Talon, who is now Most-Beloved, later returns to the Chamber of First Runes and leaves Lindsay's information at Beach's grave, deciding not to divulge the true origin of the Downside; he sees Beach's journal there, and though as tempting as it is to read it, Talon leaves it.Upon exiting the chamber, Talon tells the guards to never let anyone (himself included) in until a new Most-Beloved arises.