Sherlock Holmes: Untold: The Adventure of the Remarkable Worm Part 2 (8.2)

Aboard the Prime Minister's train, Dr Watson is telling a story, long suppressed, about a troubled young journalist, a dead man walking and a creature unknown to medical science. And while the politician listens reluctantly to this tale from long ago, somewhere in the background of it all the closing moves of a quite different game are beginning to be played out.