The four time travellers regain consciousness to find the TARDIS in semi-darkness. The Doctor has sustained a nasty gash to his forehead and the others are suffering memory losses and pains in the head and neck. Tensions mount as the Doctor tries without success to locate the problem with the ship and a series of strange events occur. The main doors open and close of their own accord; a confusing sequence of images appears on the scanner screen; and the faces of all the clocks and watches on board the ship suddenly melt.

Ian and Barbara contemplate the possibility that an intruder may have got on board, but the Doctor suspects that they themselves have sabotaged the instruments with the intention of blackmailing him into returning them to 20th-century Earth. Susan also comes to mistrust the two teachers until eventually she realises that they could not possibly have been responsible for everything which has happened. 

The danger intensifies as the ship experiences a total systems failure and its power threatens to escape. The Doctor grimly announces that they have no more than ten minutes left to live: they are on the brink of destruction!

Barbara suddenly realises that it is the ship itself which has caused the increasingly bizarre series of events that they have been witnessing: it has been trying to give them a warning, but a warning about what? The Doctor discovers that the 'fast return' switch on the control console has become jammed and that they have been rushing backwards through time towards the beginning of the Universe. With the fault repaired, the ship returns to normal.

The Doctor is forced to admit that Barbara's intuition has saved the day, and the tensions which have existed since the two teachers first pushed their way into the ship now ease a little.

The ship's next landing point is a snowy landscape, where Susan finds a huge footprint which appears to have been made by a giant!

Synopsis from Doctor Who: The First Doctor Handbook by David J. Howe, Mark Stammers and Stephen James Walker, reprinted with permission; further reproduction is not permitted. Available from Telos