The one where the Master tries to destroy Gallifrey in order to extend his own life...
Has Dr Who ever looked so beaten and bedraggled as Tom does at the start of this episode, following his fight with Goth in the water? The sight of Tom's soaked and wilting curls and his torn and bloodied clothes proves the Doctor has been through hell and back, all in order to try and prove his innocence to Spandrell - which, incidentally, he doesn't strictly do. Spandrell ends up simply believing the Doctor because of what he goes through in the Matrix, and is also willing to believe that Goth is a traitor, without any physical evidence at all. Maybe he was disposed to the Doctor's truth all along, which makes me wonder whether all the Matrix scenes were actually necessary!
Goth is sacrificed by the Master, and left burnt and charred on the brink of death. To make matters worse, the Master calls Goth a "poltroon", a word so unusual and archaic that I had to look it up (it means coward, derived from the 16th century Italian "poltro", or sluggard). The Master is nothing if not well-educated in archaic Earth linguistics...