|Series 06, Episode 06|
|Air Date||13 November 2007|
Acting on the information from Ana, the team learns that a courier with the firing trigger is boarding a flight to Tehran. Section D receives an email warning that if the courier does not arrive in Iran, a bomb will release a toxic chemical into the water supply. The email reinforces Harry's suspicions that there is a mole within the Grid and orders a sweep for bugs.
Ros is conflicted about her participation in Yalta, when she learns that they arranged the sale of the trigger to Iran in order to limit American power. Adam and Ros go undercover on the flight to find the courier. They must identify the courier, but cannot stop the flight until the threat to the water supply is eliminated. After clearing three suspects, they discover there is an extra passenger on the flight. After Jo and Malcolm prevent the chemicals from leaving the pumping station, the extra passenger is subdued and handcuffed him to his seat.
But the man dies later when the plane depressurises and he cannot reach his oxygen mask. After the plane lands, it is revealed that the extra passenger is a CIA agent and that the pilot is the courier. Adam and Ros are too late to stop the transfer of the trigger into Iranian hands. Ros's last bug on the Grid is found on the sweep by an officer who is also working for Yalta. Sholto is disappointed, but still wants to keep Ros around— for now.