When DI Poole (Ben Miller) calls the case the "curious incident of the dog who didn't bark in the night time" he is referring to a Sherlock Holmes short story, "Silver Blaze" with another dog who would usually bark and did not.
RIchard reads a crossword clue to his lizard: "Essence of an Eastern book about a Greek character". Though the lizard never answers, the correct answer is "epitome".
Aidan Miles makes his first appearance in the previous episode "Music is Murder". He can be seen sitting in Catherine's bar discussing the price of a drink just before Catherine sits down to talk with Michelle.