Benedict Cumberbatch made his long-awaited comeback as Sherlock Holmes on Wednesday, but the hit BBC series still left fans scratching their heads over how the super-sleuth managed to cheat death.

The show's creators teased fans by depicting some of the more far-fetched ways Holmes may have survived, in a nod to the speculation that has swept the Internet since he leapt from a rooftop a year ago in an apparent suicide bid.

The BBC series, starring Cumberbatch as a modern-day version of the 19th century British detective, has been broadcast in more than 200 countries since 2010.

When British Prime Minister David Cameron set up a page on China's Twitter-like website Weibo in November, one of the most popular questions he was asked was, "When is the third series of 'Sherlock' due for release?"

There were plenty of surprises for fans in the first episode of the new series, including a cameo appearance by Cumberbatch's own parents.

But some viewers complained that the storyline, centering on a terrorist plot to blow up the British parliament, was difficult to follow.

Fans delighted and disappointed alike flooded the Internet with comments and reactions.

The Times newspaper gave the episode four stars, but complained: "You wait two years to find out how Sherlock dunnit, and three solutions come along at once."

The series has helped both Cumberbatch and Martin Freeman, who plays his loyal sidekick Doctor Watson, to Hollywood stardom.

Freeman plays the eponymous "Hobbit" in the new movie trilogy.

Cumberbatch starred last year as the villain in the latest "Star Trek" film and as WikiLeaks founder Julian Assange in "The Fifth Estate". He also features in the latest instalment of "The Hobbit" as the voice of the dragon Smaug.