The new series starts with the discovery of body found in a sealed suitcase in the silt of the River Lea. With the body preserved but clearly having been there a number of years, DCI Cassie Stuart and DI Sunny Khan begin the complicated task of identifying the victim and investigating his murder.With an expensive watch found on the body the only evidence to go on, the item is sent to forensics who suggest approaching a watchmaker who may have repaired it to find out more about its owner.Meanwhile, we meet four seemingly un-connected suspects who may have a link to the victim – DI Tessa Nixon who is struggling with her loner son, nurse Marion Kelsey who works with chronically ill children, Brighton-based barrister Colin Osborne who is in the process of adopting a little girl with his husband, and teacher Sara Mahmoud who is interviewing for a new position in a school that needs turning around. How do any of them link to the victim, though, and why would one of them kill him?