MI5's mainframe has been hacked into. But Tom and his team think they have found a lead in the form of an I.T. teacher, so Zoe is sent undercover to get close to him and find out his secrets. Will they be able to stop the culprit before the inner sanctum is breached and every agents identity revealed?
Elenco: Peter Firth , Nicola Walker , Matthew Macfadyen , Richard Armitage , Keeley Hawes , Hermione Norris , David Oyelowo , Max Brown , Lara Pulver , William Hope , Anna Chancellor , Sophia Myles , Natasha Little , Richard Harrington , Shauna Macdonald , Gemma Jones , Alex Lanipekun .