Written by League of Gentlemen masterminds Reece Shearsmith and Steve Pemberton, rhe dark comedy thriller was centred on very different characters, who each received an anonymous mysterious letter claiming: "I know what you did..." in the last series.
The final episode concluded the story at Ravenhill Hospital, for the completely insane, with a huge explosion. In the new series, all will be revealed as to who managed to survive the blast.
Steve Pemberton said: "We're delighted that BBC Two commissioners have responded in the right way to the notes we sent bearing the words 'We know what you did'. We look forward to being able to tickle and terrify our audience once again - preferably at the same time."