To gamify a rerun of series 2, clues were hidden in subtitles, revealing the unreleased title of final episode of new series.

On-air teasers drip-fed fans with clues of his return to #sherlocklives, giving fans the platform to share their excitement.

Date of first episode was revealed in a stunt, driven around London written in flowers in an 'empty hearse' - the title of first episode!

Using wireWAX technology, an interactive trailer with embedded clickable hotspots created ‘rabbit holes’ to exclusive content. Hidden hotspots requiring codes to unlock revealed exclusive behind-the-scenes interviews.

The body outline stunt appeared outside St Bart's Hospital - the scene of Sherlock’s death defying illusion.

Further photos/announcements/behind the scenes/stunt sightings shared on BBC One's Tumblr/Twitter and Facebook page.

The #Sherlocklives hashtag generated more than 300,000 tweets per episode.

10.5K tweets per minute at peak.

Most tweeted about single episode of a drama series in UK

Interactive trailer:

More than 300 views per second in first hour

Over 500,000 views within 48 hours

Over1.5 million hotspot interactions

The trailer is 60 seconds long, but average time spent is 5:19

Empty hearse stunt, directing people to #sherlocklives, trended most of the day

Body outline stunt received 47000 notes on BBC One's Tumblr, shared 1000's of times on other social platforms.

The return of Sherlock on TV attracted 10million viewers – the biggest audience on New Year’s Day.