Following a tip-off, Kotaku has unearthed what looks like potential plot details, with a casting call on industry website Breakdown Express detailing a job for Valve on Portal 2, as well as listing significant facts about the role itself. Needless to say, if you want Portal 2 to be a fresh experience whenever it arrives, it's best to avert your browsers now.

The part on offer is that of Cave Johnson, an eccentric dead billionaire who was the founder and CEO of Aperture Science. "He might not know how science works, but he knows how people work," goes the casting call, before detailing, "A born salesman, a leader, an evangelist. People trust him even when his plans are clearly dangerous." Most tantalisingly, the call goes on to state that Johnson "…goes from sidekick to principle protagonist. Sarts [sic] to lose his grip on his humanity as the story progresses." According to the post, recording will start towards the end of July this year.