Jack in his travels through time the slow way encounters Sherlock Holmes in the 1890s. Nice.
Sherlock Holmes encounters the First Doctor in the course of his investigations. And, of course, logic dictates Sherlock’s willingness to believe in the improbable. (And aren’t I lucky? This one was written for me!)
I should also mention that, while not exactly crossovers, John Elliott has also written a fair few Sherlock Holmes Storytime tales for This Time Round. These feature various narrators (from Dr Watson himself to the newest Master) retelling the stories with DW characters in the roles. It is indeed as crazy as it sounds, but also a huge amount of fun.
The Coming of the Hound (The Hound of the Baskervilles).
The Speckled Band
The Three Garridebs
The Bruce Partington Plans
The Adventure of Charles Augustus Milverton
The Adventure of the Engineer’s Thumb
The Adventure of the Musgrave Ritual