The energy creature calms down after consuming the third Doctor. The Brigadier returns and is shocked to see the second Doctor. He conjectures that the Doctor has used the TARDIS to change his appearance and transport Jo somewhere.
The President wishes to end the experiment with the Doctors, but the Chancellor points out that they are facing an unprecedented danger.
The third Doctor and Jo wake on a strange planet. They explore, watched by a gel creature.
The second Doctor fills in the Brigadier on the anti-matter creature. The Brigadier decides to contact Geneva while the Doctor works out a way to neutralize the creature.
The Doctor and Jo find bits of the lab on the planet surface. They then find Bessie and drive off in her. They find footprints left by Mr. Ollis. He watches them from the cliffs.
The second Doctor constructs a device to control the anti-matter and is then called to brief Geneva HQ on events. While he's away, Benton turns the machine on the creature. It quickly rages out of control. The Doctor, the Brigadier and Benton are forced to retreat into the TARDIS.
Jo and the third Doctor find Dr. Tyler musing on the physics of the situation. They wonder who has brought them there.
Elsewhere a tall robed figure dispatches gel guards to capture them. They are easily surrounded and taken prisoner.
The second Doctor realise that his device stimulated the anti-creature rather than calming it. He tries to plan his next move.
The third Doctor, Jo and Tyler are brought to an elaborate cave to await their captor. The second Doctor works to help the Brigadier contact his men.
Tyler wants to escape but the Doctor tries to stop him, hoping to reason with their captor for their release. Tyler tries to escape but is quickly driven back.
The Brigadier is able to contact his men and finds out the gel creatures have the building surrounded. The first Doctor returns and advises the Second to switch off his force field.
The third Doctor explains to Tyler that they've been processed in some way so that they can exist in an anti-matter world. They are brought to their captor.
The second Doctor takes the First's advice and switches off the force field. First the gel guards and then the entirety of UNIT HQ vanish, falling into the black hole…