Casting 3.2 The sign of the three

Major James Sholto : Alistair Petrie - IMDB page

An ancient officer highly estimated by Watson, Major Sholto gained a lot of enemies. After a failed mission, several young soldiers died, and their families take Sholto for responsible. That's why Sholto lives now retired from active duty and life. But he makes an exception for John's wedding, and faces an unexpected hostility: Sherlock's jealousy!

David : Oliver Lansley - IMDB page

Mary's ex boyfriend still loves her. Duly summoned by Sherlock, he will have to hear a wide range of threats if doesn't stop to call her. 

Facing a "psychopath" at least as much mad as himself, David prefers to give it up at once...

Archie : Adam Graves Neal 

As other guests, Archie has been summoned by Sherlock (God knows why). At first, the highly functioning sociopath seems ill at ease with the other child. But they soon find a common topic: the various method to kill people and essential knowledge about corpses.

Janine - Yasmine Akram - IMDB page

Janine is Mary's friend and bridesmaid. She is looking for a new relationship, and soon understands how Sherlock deduction capacities can be extraordinary interesting when he "scans" potential boyfriend. Quickly disappointed about each male guest, Janine will turn her eyes upon the genius himself: why not?

Tessa - Alice Lowe - IMDB page

Tessa is an housemaid. She met a man, flirted with him, but he suddenly disappeared. Classical? Yes, except than the man never existed! Tessa looked for him, made researches, and discovered several other women who met this ghost. That's why she took contact with Sherlock.

Jonathan Small - Jalaal Hartley - IMDB page

Jonathan is the photographer at John and Mary's wedding day. Nothing to say about him, except that he shares his names with Conan Doyle's villain in "the sign of the four". Both characters have few in common, but for their hate for major Sholto.

Bainbridge - Alfred Enoch - IMDB page

Bainbridge is a model soldier. Guard at Buckingham palace, he is victim of a mysterious stalker, and calls for Sherlock's help. But it's John intervention that will save him.