In the third episode of the BBC One spy drama’s tenth and final series, MI5 receive a red flash: radioactive material has been detected at an airport.

Meanwhile, the team realise that the leaking of MI5’s assets and the foiled assassination on Russian Foreign Minister Gavrik are connected.

> Order the Series 10 boxset on Amazon.

Episode 3 airs at 9pm on Sunday 2nd October. Here are ten teasing lines of dialogue from the episode…

» ‘He’s extremely volative. We need to be careful.’

» ‘So what fresh new hell do you have for me today?’

» ‘Erin, this isn’t right…’

» ‘I don’t really know what we’re doing here.’

» ‘I’m so sorry, Sasha. I’m so sorry.’

» ‘I’m the black sheep.’

» ‘You’re quite insane, you know that?’

» ‘We can’t afford to play the long game.’

» ‘I don’t want to be the homewrecker.’

» ‘I’m sick of secrets.’