Here's a treat for armchair detectives - TV's crime-fighting hero is back as Sherlock Holmes!
There will then be three more episodes of a new fourth series.
The hit BBC show, created by Mark Gatiss and Steven Moffat, is inspired by the original stories created by Arthur Conan Doyle.
It regularly pulls in huge audiences and has been a worldwide hit, propelling its two leading men to Hollywood and, in Cumberbatch's case, an Oscar nomination.
The third series bowed out last year with Holmes appearing to shoot villain Charles Augustus Magnussen, and teased viewers that Andrew Scott’s criminal mastermind Moriarty may have cheated death and be set for a return.
Cumberbatch was such a hit in the first three series' of the show, the logic of inviting him back is... elementary.