Pcs Mel Ryder and Millie Brown investigate when Graham Ransome reports his 17-year-old son, Alistair, missing, claiming his disappearance is out of character, as he’s not an average teenager but a gifted athlete. Graham tells the officers that Alistair was last seen at a house party that Pcs Sally Armstrong and Tony Stamp have made their way to, after receiving complaints from neighbours.
As Tony learns from Simon Thorn and his girlfriend Katie Fielding that Alistair was at the party, Sally finds Stephanie Weeks unconscious after taking drugs. When Simon and Katie claim the drugs were brought in by gatecrashers, Tony and Sally fear that Alistair may have taken some. Later, an injured man is found in a park, and Mel and Millie race to the scene where they find Alistair, but they are too late.
It’s discovered that Alistair died from severe head injuries but Graham refuses to believe that his son would be involved in drugs. When questioned, Simon reveals that an old mate, Michael Fleming, came to the party with drugs and when Alistair asked him to leave, he got angry and the two had a fight. But Michael tells DC Mickey Webb that Simon is lying about the drugs and swears he did not kill Alistair.
Things start to look bad for Michael when it transpires that he and Alistair were rivals in athletics. As the case develops, officers realise that Simon and Katie are Alistair’s killers – but they don’t have a shred of evidence to prove it…