Tread Perilously enters the annual "Tread Merrily" festivities with the thoroughly British spy series The Avengers and its Christmas-infused episode, "Too Many Christmas Trees."

It's the night before Christmas Eve Day and John Steed has been having disturbing dreams about a fellow in the Intelligence section, Father Christmas, and his own reflection. Emma Peel expresses some concern, but invites him to a party at the manor home of famed Charles Dickens collector Brandon Storey. Little does she realize, though, that the source of Steed's problems awaits them at the party. Will a night dressed as Sydney Carton and Oliver Twist lead to an experiment with telepathy?

Justin pitches his own stylish 60s spy series with a low-key name: The Conversationalists. Erik proves to have better knowledge of Dickens than Justin. He also reveals the unlikely origins of The Avengers. The British Empire takes a beating. Geography Corner takes on a culinary tone as the pair both praise local eatery The Hat and warn against what it does to their stomachs. The Bond connection gets mentioned, as does The Avengers feature film. Justin ponders the unintentionally horrifying Father Christmas mask in the episode and the nature of the telepaths leads to "the slowest way to kill someone."