Mark Gatiss on surprise cameo in Lot No. 249: "I couldn't resist"

First published in 1892, Lot No. 249 was a Gothic horror story with no connection to Sherlock's adventures – so those familiar with the original story will have been taken by surprise when a 'consultant' who smokes a pipe and speaks of plans to move to London's Baker Street popped up in the TV version.

Lot No. 249 sees young academic Abercrombie Smith (Kit Harington) encounter the strange and exotic Edward Bellingham (Freddie Fox), whose arcane research into Ancient Egypt could be inspiring something terrible.

In the original tale, Smith discusses the affair with his friend, the Reverend Plumtree Peterson – but in Gatiss's adaptation, the Reverend is replaced by a figure very heavily implied to be Doyle's most famous creation, Sherlock Holmes.

"I couldn't resist," Gatiss told RadioTimes.com of the surprise twist.

"In the story, his friend is called the Reverend Plumtree Peterson – with a name like that, [the character] promises a great deal and then doesn't really do much... and I just thought, 'Oh, I know!'."

In an earlier draft, the character was definitively stated to be Sherlock Holmes, though Gatiss later removed any direct confirmations to leave the character's identity more ambiguous.

"In the original script, Smith says 'It won't do, Holmes, it really won't.' – and I thought, no, I'm not going to say it's definitely him."

The character, credited only as "The friend", is played by actor John Heffernan, who Gatiss previously worked with on Dracula – he was cast in Lot No. 249 in part due to his resemble to the iconic sketches of Sherlock Holmes made by artist Sidney Paget.

"He looks like the Paget, doesn't he?" Gatiss said. "He just leapt into my head."

Lot No. 249 also features another Holmes reference too, though you likely missed it. In one scene, Bellingham is holding a book bearing the title 'The Dynamics of an Asteroid', a tome written by Professor Moriarty in Conan Doyle's stories.

However, the book is never clearly glimpsed on-screen – a result of a tight shooting schedule that also saw a Doctor Who Easter egg obscured in Lot No. 249.

"The book that Freddie's holding is 'The Dynamics of an Asteroid', but you can't really see it, because there's no cutaway," Gatiss explained.

Read more:

• Mark Gatiss explains why he changed the ending of Lot No. 249
• Mark Gatiss fears Lot No. 249 may be his final Ghost Story for Christmas

A Ghost Story for Christmas: Lot No. 249 is available to watch now on BBC iPlayer.

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