Zafar "Zaf" Younis joined Section D in the series 3 episode "The Suffering of Strangers," when MI5 officers Fiona Carter and Danny Hunter are being held hostage by terrorists. Zaf is an MI6 officer who had worked with Adam Carter (played by Rupert Penry-Jones) before Adam transferred to MI5. Zaf assists in saving Fiona's life, but Danny is killed by the terrorists. With Danny's death, Adam asks Zaf to join Section D.
Midway through series 4, the show gains another new character, the recruit Jo Portman, played by Miranda Raison. There is promise of a growing relationship between Jo and Zaf, but this is never fully developed. Through the following series' Zaf becomes an integral part of Section D, working closely with Jo and Adam particularly.
At the start of Series 6, Zaf is kidnapped by a group of international mercenaries called the Redbacks who kidnap intelligence agents for paying customers. The team start investigating Zaf's kidnapping, and Harry gives Ros Myers 24 hours to find him. A lead that indicates French Intelligence may know his whereabouts proves to be a trap set by Yalta as a way to try and recruit Ros. Ros is then given evidence that Zaf is dead, but this is not absolutely confirmed until the end of the series when Zaf's body is found in Pakistan and it is revealed that he was tortured to death by several clients of the Redbacks.