A family in Wales are defrauded by what appears to be a Nigerian internet scam, but it tracks to an office in Lewisham, South London. DCI Catrin Sayer, Metropolitan Police, believes the case belongs to the local borough detectives, not to her specialist team in Operation Undertow. Commander Karen Moore decides otherwise. Sayer’s reluctance evaporates when a police officer is seriously injured. As the violence escalates, she is forced into a central and very personal role to bring closure to the investigation.