Daniel has travelled to prehistoric times and seen the dinosaurs up close, but he's promised his old friend Ole Pederson not to try it again, because it's just too dangerous. What would they tell his parents if Daniel never came back? But Ole's friend Mildred Roost, a prominent palaeontologist, wants to go back with Ole. For them the trip will be the thrill of a lifetime, seeing up close the collosal creatures they've spent a lifetime studying. Deep down Daniel knows that they accept the risks: they could even die on their journey, deep in the past. Who could have guessed they'd end up in the time of the dinosaurs' final extinction? That they'd see sights more amazing and terrible than they could ever have imagined? When they don't come back on time, Daniel faces a dilemma. Should he keep his promise or should he go back and help them?