[user104658]

Richard Roxburgh? Jesus christ Nicky - he's 60! Frank is meant to be in his 20's... he's in a sexual relationship with Rachel Amber and whilst it's meant to be a bit inappropriate with the age gap (she was I think 17 at the time their relationship started) he's not meant to come across as an actual paedophile .

I'd go with Dacre Kayd Montgomery-Harvey (Billy from Stranger Things) - his role in Stranger Things also shows he could play the character well. Make him pale with a scruffy goatee and that's your Frank.