Fans left reeling by shocking twist in Inside No 9's The Stakeout

The Stakeout played on the cliches of procedural police dramas, introducing us to PC Thompson (Steve Pemberton) and his rookie partner SPC Varney (Reece Shearsmith).

Thompson is shaken, having recently lost his previous partner in a violent attack, the circumstances of which are gradually revealed over the course of a tense half-hour.

The truth comes out that Varney is a vampire and turned Thompson's former colleague into an undead monster, who makes a frightening return at the end of the episode.

Inside No 9 is a show built on jaw-dropping twists, but fans were particularly taken aback in this case, praising a script laden with hints and clues - including the title itself.

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In the episode, the two officers play a word game in which two people improvise a story, but can only start sentences with the words fortunately and unfortunately.

This format was adopted for a number of fan tweets, including one from Detectorists star Rebecca Callard, who had a small voice role in the episode.

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On Monday, the BBC announced that Inside No 9 would be returning for another two series, each consisting of six new episodes.

Series creators Reece Shearsmith and Steve Pemberton said: "We are delighted and exhausted in equal measure at the prospect of two more series-worth of tall tales and fearsome fables. However, we will endeavour to showcase the very best of what the BBC can do in every genre with 30 minutes of story-telling and some half-decent wigs."

No premiere date has been announced for the new episodes, but given the two-year gap between series four and five, it would be wise not to expect them too soon.

Inside No 9 is available to stream on BBC iPlayer