Dimitri Levendis was born in North London on March 17, 1974 to Greek immigrant parents, and formerly served as a soldier in the SBS, but left in unknown circumstances. He consequently joined MI5 as their Piracy and Terrorism Case Officer.
In the first episode of the series, Dimitri is undercover as the captain of a freighter leaving Tangiers and carrying Somali terrorist Hussein Abib (Peter Bankole). Lucas boards the ship to assassinate Abib, but before he is able to complete his mission, the ship is hijacked by Abib and his men. Dimitri discovers that the terrorists have loaded the ship with explosives, apparently with the intention of sailing into Plymouth where an aircraft carrier is about to be launched. Lucas encounters private contractor Beth Bailey, masquerading as an Eastern European prostitute, and the two escape. Dimitri and his crew are held hostage by Abib, who executes one of them for failing to change the ships course. Dimitri and his surviving crew member are moved to a storage container, were he tells the man that he is an MI5 agent. While there, they hear two boats go overboard, later discovered to be submersibles laden with explosives meant to explode the Thames. After escaping from the storage container, Dimitri kills Abib and makes it back to Britain.
In the next episode, after MI5 receive intelligence that the Nigerian government plan to assassinate oil baron Robert Westhouse, Dimitri and Lucas infiltrate his mansion to place a bug in the house. It becomes apparent that Westhouse plans to buy chemical weapons to launch at Lagos and precipitate a coup in the country. Dimitri works with the team to identify the assassin, later revealed to be Jacob Chapman, and then goes with Lucas and Beth to support Harry Pearce as he retrieves the weapons from Westhouse.
Over the following episodes Dimitri works with the team to foil an FSB double cross and assist the Azakstan government in fooling the Russians into believing they have a biological agent called Paroxocybin. Dimitri and Lucas break in to the Chinese embassy to steal information on a trio of Chinese Intelligence agents enter the country, and are only saved from capture by asset Kai, a Chinese diplomat turned by Beth. When the Chinese later plant a bomb in central London and threaten to detonate unless scientist Dr Jiang (Daphne Cheung) is handed over to them, Dimitri finds and disarms it with help from Tariq.
Dimitri goes undercover in episode 5 to join an Israeli peace delegation who are attending talks in London with the Palestinians and chaired by the Americans. The peace talks are threatened when a plot is uncovered to assassinate the American President, first thought to be the work of a Lebanese militant. Dimitri builds a relationship with Anna Cohen, the daughter of the lead Israeli negotiator, and talks her out of blowing herself up when she is revealed to be the actual assassin.
In episode 6 Dimitri is sent to the Thames to assist the police bring in a mafia boss who is giving himself up.
In the series finale, Dimitri joins the manhunt led by Harry for the rogue Lucas and Maya Lahan. Dimitri and Beth take part in a manhunt led by Harry to pursue a rogue Lucas and Maya Lahan. In a shootout with the two MI5 agents, Maya is fatally wounded causing Lucas to threaten to detonate a bomb in a busy train station unless Harry meets him, alone, at the top of a nearby building. After commotion at the bottom of the tower, Dimitri and the rest of the team are left visibly upset, with Lucas' fate unrevealed.