When Liz learns from one of her agents that suspicious meetings are taking place at an Islamic bookshop, she trusts her instinct that a terrorist cell is at work. Her boss, Charles Wetherby, Director of Counter Terrorism, trusts her as well and immediately puts a surveillance operation into place. An attack seems imminent. So Liz is surprised when Wetherby suddenly takes her off the case. And she's shocked to hear the reason why: he has received a tip-off that a mole is at work inside British Intelligence.