Jack's (Sam Claflin) sister Hayley (Eleanor Tomlinson) is about to get married to her Italian sweetheart, Roberto (Tiziano Caputo). Sam learns that Dina (Olivia Munn), whom he met a year earlier but never had the chance to tell her how he felt, will be attending. With his best friend Bryan (Joel Fry) standing in as Hayley's maid of honor, how can this be anything but an extra special day?
However, when Hayley's crazy ex-boyfriend arrives high on cocaine, things begin to unravel. She tries to make things better, but they only get worse. But wait. What if just one thing had changed and it all went differently? We get two different versions of how the wedding day plays out, with plenty of laughs along the way.