At the end of the episode, Dr. Bullard (Barry Jackson) declares his intention to go on a fishing vacation in Ireland. After John Nettles's departure from the series, Jackson told producers that he too would leave, unless his character got more screen time, and this episode was Jackson's final appearance. He died of cancer on December 5, 2013.
The old staircase at Malham Hall within the staff residence, at the top of which Freddie's and Dominic's bedrooms are located, is the same staircase where Jeff Bowmaker hosts his ghost tour at in The Silent Land (2010).
When Jones calls Barnaby from the Oblong Foundation and complains that "They are a bit scary to be honest", Barnaby answers: "England expects, Jones!" This is a shortened version of the phrase: "England expects that every man will do his duty". It was a signal sent by the Vice Admiral of the Royal Navy, Horatio Nelson, to his troops on 21 October 1805 while getting ready for the Battle of Trafalgar against the French forces of Napoleon. The phrase has been regularly quoted, paraphrased or referenced. It has its own Wikipedia entry.
The Eight bells pub used as a filming location in this episode was also used in the episode "Blood in the saddle".
Holly Aird will also appear later in story The Blacktrees Prophecy.