The Undeclared War

Danny deals with the aftermath of the Russian cyberattack, with Saara making a shocking discovery about how the Russians broke into the GCHQ system.

Danny and Roz clash, and Saara uses coding expertise to help Charlie begin to search for the mole. Vadim tries to escape from Yin Technologies.

Barbara crosses paths with her ex-boyfriend, Nicky Chan, first in 2014 in Hong Kong, and then again in 2022, when he reappears in London.

Malware causes havoc in government departments, Danny and Roz reluctantly work together to find out what is going on.

Barbara comes under Charlie's scrutiny. Danny and Roz work together to get Vadim to safety so he will hand over the ciphertext.

Danny confronts Barbara - the truth comes out. Roz and the team must race against the clock to find out what the malware is searching for.