The London Deep series is set in the future in a flooded London, where rival police forces for children and adults compete to keep the peace. London is menaced by a mysterious plague. The disease, which leaves a spider web pattern of fine lines upon the victim, has been nicknamed 'Threadneedle'. The YPD order a full scale evacuation of London, claiming that adults are the carriers. When her father is taken to a 'Safeguarding' centre, Jemima Mallard enlists the help of a team of mercenaries to bust him out.