During Series 1 of Ashes to Ashes, Caroline Price is revealed to have had an affair. All parties agree to keep the matter secret from Tim Price to spare the family. Yet in 'Episode 8', Tim Price has learned the secret, which is the motive for his subsequent actions at the close of the series. How and at what point does Tim Price learn of Caroline's affair?
We don't know.
The mystery around Tim and what he knows is a plot device, because:
his role in the death of the Prices in concealed from us until the end of this episode.
Hints are dropped during Episode 8 that Tim found out about the affair either while he was away, or immediately upon returning.
Tim behaves darkly towards Evan during a court scene, and then has the following exchange with Alex:
ALEX: Evan could take over your caseload. TIM: He's very - You know Evan? ALEX: I do. TIM: A very charming man. Very, er, charming.
When Alex arrives at the Price house to make an arrest, she overhears part of a conversation reflecting some sort of difficulty in the Prices' marriage:
CAROLINE: Tim, all I'm saying is, sometimes people have to move on. That's all. TIM: When you walked into the common room that first morning, I felt we'd be together forever. I was 18. CAROLINE: We're not undergraduates any more. We change or we die. TIM: Forever and ever.