The Master (Roger Delgado) in the guise of a Professor, penetrates the Newton Research Institute in Wootton, near Cambridge. He conducts experiments in transmitting matter by converting it to light waves, using a trident-shaped crystal to summon a being he calls Kronos. The Doctor and Jo visit the institute, believing that the Master’s TARDIS is there, judging by the way it disrupts the normal flow of time. In particular, one research student named Stuart Hyde (Ian Collier) has suddenly aged eighty years. Later, Sergeant Benton (John Levene) is changed into a baby. Brigadier Lethbridge-Stewart (Nicholas Courtney) orders an evacuation and searches for the Master. As the Doctor explains, Kronos is a Chronovore, a creature that feeds on Time, attracted to the vortex to ancient Atlantis using a crystal trident like the one the Master has, but larger. The Doctor believes the universe will be in danger if the Master gains control over Kronos.
Krasis (Donald Ecclis) the Atlantean High Priest of Kronos, is taken through time to an office at the institute, where the Master uses the Seal of Kronos to conjure Kronos, who appears as a white avian figure and devours the director of the institute, Doctor Percival (John Wyse). Kronos is only briefly controlled by the Master and breaks free when Krasis realizes the Master only has a small crystal. Make up your own joke about crystal envy. The UNIT convoy bringing the TARDIS on a flatbed truck to the Doctor is waylaid on the road by forces out of time marshalled by the Master—armies with historical weapons, and a WWII buzzbomb. The Doctor and his team build a time-flow analogue to interrupt the experiments. The Time-Lords confront each other in a time-duel with their TARDISes, causing all kinds of amazing temporal effects. The Doctor is thrown into the vortex, but Jo and the TARDIS save him.
In ancient Atlantis, King Dalios (George Cormack) worries about the disappearance of Krasis and the threat to the Kronos crystal, guarded by the Minotaur (David Prowse) in the maze—yes, that David Prowse. The Master seduces Queen Galleia (Ingrid Pitt). When the Doctor and Jo arrive, the king tells them the Atlanteans sought to destroy the crystal, fearing the chronovore, but only splintered it. The Doctor Faces and destroys the Minotaur to Save Jo in the maze, but the Master has taken over the throne. Jo and the Doctor are forced to witness the King’s death by trident.
Krasis uses the crystal to summon Kronos, who begins to destroy Atlantis. This is the third time in the Doctor Who canon that Atlantis is destroyed, each for a different reason. The Master gayly buggers off and flees in his TARDIS, with Jo as his prisoner. The Doctor pursues in his TARDIS, and finally resorts to a time-ram, in which both try to occupy the same space at the same time. This frees Kronos, who saves the Doctor and Jo in gratitude, but the Master escapes. The Doctor and Jo return to the institute and put an end to the Master’s dangerous experiments. Sergeant Benton is restored to his correct age, but without his clothes.
The interior of the TARDIS was re-designed for the story. The BBC was still, somehow, erasing tapes, but this time they were saved by TVOntario. The story did not get rave reviews and much of it was considered silly. But there were some interesting timey-whimey effects. For one thing, the Doctor, lost in the vortex, speaks to Jo through the TARDIS telepathic circuits. For another, the Doctor, pursuing the Master, attempts to land inside his TARDIS, but something goes a bit wibbly-wobbly and they land inside each other, that is TARDIS One is inside TARDIS Two, but TARDIS Two is also inside TARDIS One. I love this stuff.