Glasgow's citizens are in celebratory mood for the annual West End Festival parade. But beneath the jovial surface lurks something darker. A confused young woman is found wandering among the stilt-walkers and jostling crowds, claiming to have been abducted by aliens. Before DCI Anderson and DI Costello can investigate further, a body is discovered and it becomes horrifyingly clear that a depraved killer has taken advantage of the busiest day of the year to carry out a gruesomely macabre plan.