He is first seen singing along with his Walkman at a party aboard The Lady Di on the morning of 7 July 1981. He manages to avoid the uniformed police officers raiding the party. Accusing Alex (whom he thinks is a prostitute) of calling the police, he angrily pulls her about and intimidates her until the flashy arrival of DCI Hunt, DS Ray Carling, and DC Chris Skelton in Hunt's Audi Quattro.
Gene Hunt's first line in the series is directed to Markham whom he tells, "Today, my friend, your diary entry will read, 'Took a prozzi hostage and was shot by three armed bastards.'" Alex uses her hostage negotiating skills to convince him to surrender, lest he be shot by Hunt and his men. His head is twice slammed into the Quattro by Carling during the arrest. In custody, Carling confiscates Markham's Walkman and gives it to WPC Shaz Granger.
Despite Hunt's certainty that Markham is a drugs kingpin, Drake immedately sees him for what he truly is: a low-level front-man for a real drugs lord, as he lacks the requisite inclination toward delegation. "Top flight crime lords," she explains to Hunt, "expect their minions to do their donkey work. They expend their energy only when it's absolutely necessary. Crime lords don't gloat at police stations, Gene. They don't spend money on expensive lawyers and then do all the talking themselves, and they are not out to impress Northern flatfoots like you."
While his boss, Arthur Layton, is in custody, Markham attempts to shut down their supply line through a series of nine payphone calls and a message picked up on Charterhouse Lane near Tower Bridge. He is picked up again - now clad in a cliché 1980s ensemble of double-breasted pinstripe suit, blue shirt with white collar & cuffs, and yellow 'power tie' - and agrees to speak with Hunt ... alone. He is released shortly thereafter, having puported to give Hunt the entire network.
Drake sets a trap to prove Markham works for Layton. She has Skelton and Granger stake out the message drop, having planted an envelope for Markham to take to Layton. While Skelton goes to urinate, Markham captures Granger. After beating Skelton, Markham and his henchmen leave with Shaz as insurance that CID will not interfere. Drake's plan to connect Markham to Layton works, however, as the car in which Markham takes Granger is found to be registered to Layton.
CID find Markham, Layton, their gang, and Granger at a large drugs deal at the docks near Tower Bridge. During the ensuing gunfight, Markham attempts to flea in Layton's Mercedes which Hunt immobilises with a well-placed shot to its radiator; whereupon, Markham fleas on foot. Having taken time to gather up several kilograms of cocaine, he is caught by Skelton. Markham's cocky attitude backfires when he taunts the armed Skelton about not being the sort of man who can pull a trigger; Skelton shoots him in the foot.