At GCHQ, Danny's under pressure dealing with the fallout from the Russian cyber-attack when a bold new threat emerges.

Vadim finds himself working in captivity for the Chinese. At GCHQ, Danny and Roz clash over China, and the mole hunt continues...

When Barbara's charming ex-boyfriend, Nicky Chan, re-appears in her life, she is forced to make an impossible decision.

While Danny becomes increasingly concerned about Barbara's erratic behaviour, malware causes havoc across government departments.