March 1895. Hilary Term at Oxford. In the newly built extension to the University Galleries, Professor Quantock has put the finishing touches to a wondrous computational device which, he claims, is capable of analytical thought to rival that of the cleverest men alive. Indeed, his so-called Thinking Engine seems equal to Sherlock Holmes himself in its deductive powers.

To prove his point, Quantock programmes his machine to solve a murder in the Jericho area which has been baffling Oxford police. The Engine identifies a suspect who proves not to have a valid alibi for the night of the crime. The man is duly arrested and arraigned.

Sherlock Holmes cannot ignore this challenge. He and Watson travel to Oxford, where a battle of wits ensues between the great detective and his mechanical counterpart as they compete to see which of them can be first to solve a series of crimes. As man and machine vie for supremacy, it becomes clear that the Thinking Engine has its own agenda. Holmes’s and Watson’s lives are on the line as a ghost from the past catches up with them...