In the first scene, in which Sherlock and Alfredo are watching Abbott and Costello's famous "Who's on first?" sketch, Sherlock mentions that he has the film where they meet Frankenstein. In Danny Boyle's stage production of Frankenstein, Jonny Lee Miller played both The Creature and Victor Frankenstein, roles he shared with Benedict Cumberbatch, the modern Sherlocks alternated roles for each performance.
In this episode, Michael Weston plays Oscar--a drug dealer from Sherlock's past looking for his sister Olivia. Weston played Simon in Law and Order: SVU, Olivia Benson's brother.