Coronation Street actor Bill Roache is the only cast member who knows who really pushed his character Ken Barlow down the stairs.
The ITV soap creators have told viewers that Friday night's episode will see builder Pat Phelan top the suspect list after police decided that Ken's fall on Monday was no accident.
But according to the Mirror, Roache is the only member of the cast who knows for sure if Phelan is the culprit.
As Ken continues to fight for his life in hospital, a source told the paper: "Bill has just had another batch of scripts sent to him, so he now has worked out who it is.
"For now Bill is keeping his lips sealed about who is the guilty party.
"It is the source of lots of conversation backstage at the moment."
They added that many of the soap's actors have asked to be kept in the dark so it does not affect how they act on screen.
As the story developed on Wednesday, viewers also began to sense Phelan (played by Connor McIntyre) may be the most likely attacker, with one commenting on Twitter: "It's probably Phelan who attacked Ken, but maybe that's what they want us to think! #corrie".
In Friday's show, police finally arrest McIntyre's character after his name crops up in interviews with the Barlow family and they learn about his earlier row with Ken over an unfinished kitchen.
Phelan had been working in Ken's home in the lead-up to the moment viewers saw the Barlow patriarch suddenly tumble down the stairs, landing unconscious.
But the Coronation Street Twitter account is still inviting fans to vote on who they believe it was, offering up family members Adam, Peter and Tracy, Daniel Osbourne and Sinead Tinker as suspects, as well as Phelan.