Adric is caught and used by the Master to interfere in the Doctor's recovery after the regneration. Adric sets the console under the Master's control to go to Event One-the creation of the galaxy by a huge inrush of power. Avoiding that--the TARDIS lands on Castrovalva--a small, gentle type world. Here, Tegan and Nyssa help the Doctor rest. They find Castrovalva has a secret--it was only just created by Adric under the Master using the Logolpolis computations. It is a closed universe which folds in on itself. The Doctor pulls Adric from the Master's neural net and they escape but Castrovalva collapses. 1981. Earth sequence begins Feb. 28, 1981. also possibly set on Castrovalva in 2480 or 5450.