The sentient Space Station Computer Five, corrupted by Time Lord directives, enforces lethal security protocols, turning life support against its crew to eliminate 'threats' to temporal research.

The bridge crew identifies three approaching Sontaran battle cruisers on defensive screens as Doctor and Peri materialize beside a falsified lake. Before any action can be taken, Chessene secretly disables …

The Doctor and Peri arrive on the compromised space station amid signs of recent violence. Peri urges retreat, but the Doctor insists on uncovering the truth despite the evident destruction. …