Peter and Carla's affair is exposed next week when pictures of the pair kissing are handed to Leanne (Jane Danson) at Frank Foster's rape trial.
In the aftermath of the revelation, Leanne has a long heart-to-heart with Peter and eventually admits that she might be willing to stay with him - as he forgave her own affair with Nick Tilsley (Ben Price) last year.
Leanne's words leave Peter to make a decision over whether he wants to fight for her, or pledge his future to Carla (Alison King) instead.
Gascoyne told Inside Soap: "There's an awful lot of talking to be done. Peter and Leanne have a dark night of the soul, where everything comes out in the open - and Peter is left with a huge decision to make in the end.
"It's not what you might predict, though - there's a twist in those scenes that's quite unexpected. I think they're very well-written."
Gascoyne also confessed that Peter might be tempted to take revenge on Carla's behalf if Frank (Andrew Lancel) is found not guilty at his trial.
"I reckon he'd want to kill Frank," he confirmed. "And you'd never know with Peter. He might have a moment of madness - especially if he's been at the bottle again."
Coronation Street continues on Thursday at 8.30pm on ITV1.
> Coronation Street character to be killed off?
> Coronation Street trial shocks, EastEnders dancing, Emmerdale warning, Hollyoaks newcomer
> Read more Coronation Street spoilers and news
Watch a preview of Thursday night's Coronation Street episode in the video below: