Jules and Holly have been best friends since university. They tell each other everything - trading revelations and confessions, and sharing both the big moments and the small details of their lives: Holly is the only person who knows about Jules' affair; Jules was there for Holly when her husband died. And their two children - just four years apart - have grown up together. So when Jules' daughter Saffie accuses Holly's son of a terrible crime, neither woman can possibly be prepared for what this means - for their families or their friendship. Especially as Holly refuses to believe her son is guilty. For fans of He Said, She Said and Anatomy of a Scandal, Penny Hancock's I Thought I Knew You is about secrets and lies - and whose side you take when it really matters.