John Casterman

John Casterman is a non-canonical character created for the 1995 ITV TV film adaptation of Hickory Dickory Dock. Casterman is an Assistant Collector of H.M. Customs and Excise. In the episode, he leads an investigation into a diamond smuggling network masterminded by Christina Nicoletis. Casterman knew Mrs Nicoletis was behind the operation and was probably using the network of student hostels and other businesses which she owned. He suspected that students staying at the hostels were being used in the actual smuggling but did not know how it was done or which specific students were involved. As part of his investigations, he sent an agent Sally Finch undercover into the hostel at Hickory Road posing as a student. This customs investigation intersected with a investigation run by Chief Inspector Japp and Poirot into the murder of Celia Austin at the same hostel. As Japp and Poirot began to probe deeper and deeper, the position of Sally Finch became endangered and Casterman was obliged to take Poirot into his confidence.

Casterman's character is used to create suspense in the episode. From the beginning he is often seen as an unknown sinister figure conducting surveillance on the students or the hostel, even working as a shop assistant at the rucksack shop opposite the hostel. Not until near the end of the show does the viewer come to learn that he is a Customs official conducting an undercover investigation. The character of John Casterman is played by Granville Saxton.