Morning rush hour on the London tube.

Laurie Bateman witnesses a terrible accident. Life had been looking up - she's dating a new man and finally getting praise at work. But after the accident everything seems to plummet downhill.

In the space of a few days her flat is burgled and her flatmate assaulted - she loses her phone and then her job. Are these events linked? Perhaps what she had seen was something more sinister?

Compelled to investigate, Laurie finds herself in serious danger and is soon fleeing for her life through tube tunnels in the dead of night - the hunter has become the hunted.