Season 4, Episode 5:
Harry mourns the suicide of a retired MI5 officer until a journalist informs Harry the officer was murdered because he'd been about to sell his autobiography and expose a lifetime of service secrets. The journalist is taken under MI5's protection as the team investigate. The trail leads them back to Whitehall and Juliet where Harry is informed of the real politick; either one elderly officer died or the whole service was brought down. Harry can do nothing but protect his team from further assaults from this rogue Whitehall cabal. He threatens to publish the officer's memories should anything like this happen again.
Missed this one? Trying to catch up? Read our recap of this episode here.