Quiz tells the story of Charles Ingram, a former British army major, who caused a major scandal in the early 2000s after being caught cheating his way to winning £1 million on the game show Who Wants To Be A Millionaire? It tells how Ingram, his wife Diana and an accomplice, Tecwen Whittock, who was sitting in the audience, initially pulled off the on-screen heist before being caught and standing trial.

When her husband, Lee, is murdered, Sarah Manning comes to realise that she knows nothing about his past. Sarah begins to question who Lee actually was and what he did in his work for a powerful global organisation. And why did Lee, a salesman, need to carry a gun?