The North-West Underwater Search and Marine Unit covers six police forces from the bottom of Scotland to the bottom of North Wales. When their police boat is crushed in an incident, Inspector Dave Corcoran calls on his best mate, John Heussi, to turn what looks like a tug boat into a police vessel. John is only too happy to accept the challenge.Meanwhile, back at the Vehicle Maintenance Unit, the team have to fix up a beat car whose tyres were slashed whilst on duty, John's favourite vehicle is returned in a less-than-pristine condition, and there's an ongoing investigation into Darren's facial hair.