In the beginning of the episode, a couple that appears to be affluent are walking with their son at night. It closely resembles the situation shortly before both of Bruce Wayne's parents were murdered.
First mention in the series of Gotham City. This occurs when Thomas Wayne meets Martha Kane for the first time (the two would ultimately marry and have Bruce Wayne).
The news presenter mentions Cliff Richard and The Shadows splitting up to pursue separate careers. This happened in 1968 placing the episode in that year.
When Alfred and Martha are having tea at The Darkness, Martha asks him if he's afraid the tea might be poisoned. Alfred says no, because the proprietor isn't Italian. Jack Bannon, the actor who plays Alfred, previously played Angelo Poliziano in "Medici", a character based on an Italian poet who died of arsenic poisoning.