30 Days of Blake's 7 - day 2

Day 2: Favourite episode

This one's harder, but I'll go for Killer. It has excellent Avon and Vila, two of my favourite guest characters (Bellfriar and Gambrill), a good plot with no holes (looking at you, Mission to Destiny, to mention an otherwise excellent one) and the first time I saw it, I went cold all over at the ending.

Anyone else have one? 

All the questions are on Tumblr.