The Doctor realises the Master is trying to harness the power of Kronos, last of the Chronovores, but is unaware Percival is harbouring him at the institute.

The Master enlists the help of Krasis to control Kronos while Yates tries to bring the TARDIS to the institute only to come under attack from dangers from the past.

The Master prepares to travel back to Atlantis but the Doctor links his TARDIS to the Master's to try and stop him.

Both TARDISes reach Atlantis, where the Doctor befriends King Dalios while the Master enlists the help of Queen Galleia to try and obtain the crystal of Kronos.

The Doctor enters the labyrinth to try and protect Jo from the minotaur but the Master has seized control of Atlantis and prepares to summon Kronos again.