A hotel guest book provides police with the names of members of an international drug smuggling network. Eagle-eyed officers match a hotel in Portugal to a selfie posted on social media by someone they suspect is a mule for the gang and are then able to make multiple arrests. Elsewhere, a gang of thieves who made off with £20,000 worth of perishables from a food factory are brought to justice after a car number plate left near an abandoned trailer allows them to be traced across the country.

A jacket recovered from a suspect's home is found to have the DNA of two stabbing victims on it as police hunt for the person behind a series of seemingly unprovoked attacks. There's little for police to go on after a man is left to die in the street, and when the attacker strikes again, they are in a race against time to find the person responsible.

Elsewhere, a fingerprint found on the number plate of the getaway car used in the armed robbery of a neighbourhood pub leads police to their suspect.