On Zolfa-Thura, Meglos plans to steal the ancient and powerful Dodecahedron from the neighbouring world of Tigella. But first, the Doctor must be prevented from interfering.
On leave from the Western Front, James carelessly complains about shortages and is drawn into a political intrigue. Daisy and Edward announce their engagement.
While Meglos escapes with the Dodecahedron, the Doctor is mistakenly held responsible for the theft and is sentenced to a gruesome death as punishment for his crime.
The Doctor must convince the Tigellans of his innocence if he is to prevent Meglos from using the dodecahedron to destroy their world.
Simon interrupts an armed robbery and is told by Teal that the gang in question are are building up to a last big job.