Can you always believe the people you love? 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's 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's daughter Saffie accuses Holly's son Saul 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.