Charlie explains to Sarah on the third anniversary how he got paired with Rex, as his K9 handler was semi-accidentally shot dead while chasing a kidnapper in the forest. Rex wouldn't leave his master nor allow forensic investigation, until Charlie made friends with food and kindness. The K9 command was to put Rex down 'standard practice', but Charlie got permission at least two day to track down the kidnapper and missing pre-teen, who turn out the stake of a battle between a false ID mother on the run, traitor art teacher and ex-con father's henchman. Rex does great and finds a new home on Charlie's couch and the station furniture, sanctioned on trial by the K9 and chief Donovan appointing single-living Charlie his happy handler.
—KGF Vissers