*Warning – contains full spoilers for The Undeclared War season 2 episodes 1-6. *AdThe second season of The Undeclared War kicked off with the discovery that a mole within GCHQ had allowed the Russian's access to execute their devastating cyber attack from season 1. Siân Brooke as Barbara Napier in The Undeclared War. Accept and continueBrooke joined the cast of The Undeclared War for season 2, which has arrived four years after the first season aired. The Undeclared War season 2 is available to stream in full on Channel 4 now.