The Doctor is forced to help the Master control the mind parasite while Yates finds out where the Thunderbolt has been taken only to be captured by the Master's men.
Did You Know?
The colour master videotape was wiped by the BBC in the 1970s and although colour versions were sold overseas, only 16mm black-and-white film prints were retained by BBC enterprises. However, this episode was restored to colour for the DVD release in 2013 using the chroma dots discovered in the film prints. See more