The BBC has released the synopsis for the second episode of Sherlock’s third series, The Sign of Three.

Sherlock faces his biggest challenge of all – delivering a Best Man’s speech on John’s wedding day!

But all isn’t quite as it seems. Mortal danger stalks the reception – and someone might not make it to the happy couple’s first dance. Sherlock must thank the bridesmaids, solve the case and stop a killer!

Benedict Cumberbatch returns as Sherlock Holmes, with Martin Freeman as John Watson, Mark Gatiss as Mycroft, Rupert Graves as Inspector Lestrade, Una Stubbs as Mrs Hudson, Amanda Abbington as Mary Morstan and Louise Brealey as Molly Hooper.

It airs Sunday 5 January at 9pm – 10.30pm.