Osgood and Captain Josh Carter are sent to investigate the disappearance of a UNIT scientist. Meanwhile, alien technology has fallen into the hands of Lyme Industries, and Kate Stewart can't persuade the company's CEO to give it back.
With few people left to trust, and with assassins on their tail, Kate and Osgood race to UNIT Command in Geneva. Will General Avary be able to help them?
The threat is now clear, and Kate Stewart retreats to UNIT HQ with her most trusted colleagues. She has no choice but to place the Black Archive into lock-down, and the Tower of London is where UNIT will make its stand.
Caught between human greed and an unstoppable alien power, Kate Stewart leads her closest allies on one final, desperate mission. This could be the very last chance for the human race.