Lane, Standing, Halford and boss Pullman return to put their collective experience to more good use.
They may have handed in their badges and collected their pensions years ago, but Lane, Standing and Halford still work at the London Metropolitan Police as civilians investigating unsolved crimes as part of boss Pullman's team, Unsolved Crime and Open Case Squad (UCOS).
Led by Pullman, who spends half her time trying to rein them in, the three men investigate an array of challenging and disturbing crimes. You'd have to be very brave to tell this motley crew they are too old to chase criminals.
Whatever they lack in agility, they more than make up for in their years of experience. Out of touch with modern policing, Jack, Brian and Gerry thrive on bending and even breaking the rules to get a result; something which certainly annoys Pullman.
The question is: will Pullman stop them or join them in doing just about anything to get to the truth?
Amongst the cases the team have to deal with in the fourth season: they head to the big top to investigate the murder of a circus owner and ringmaster, and look into the case of a rich old lady who loved her cats more than her relatives, leaving the cats all her money in her will.
The series is produced by Wall to Wall.