Adric, Nyssa and Tegan aid the Monitor in saving the Doctor after he is trapped inside his shrunken Tardis. The Master, posing as Nyssa's father Tremas, makes his presence known on Logopolis as his plan nears it's completion.
With Nyssa from Traken unexpectedly rejoining the group, Adric aids the Monitor of Logopolis in trying to save the Doctor before time runs out. The Master, at liberty to prepare, is finally ready to reveal his true target, which unknowingly sets off the biggest catastrophe of all time.—statmanjeff