A tiny newborn baby is abandoned in the toilets of a Yorkshire hospital. At the same time, the Trans Pennine commuter train is halted by a suicidal jumper - are they connected? From this moment on, the lives of those on board the train and in the hospital will be changed irrevocably, not least for DC Laurie Franklin (Suranne Jones), off-duty that day but travelling on the train with her mum, Jen (Anne Reid), who has recently been diagnosed with Alzheimer's. Laurie likes tying up loose ends. And, if she can prove a connection between the body and the baby, she will be happy. But things never turn out quite the way we expect. Who is the baby's mother? And who is the jumper? And was it a suicide - or was it really a murder? As Laurie is drawn deeper into the mystery, she realises this might not be a simple case at all, but something much darker. Her life becomes even more complicated when she falls for one of her work colleagues David Morrissey who is a hard nosed Detective with a strong will.