For seven years, Mark Stone was a dynamic environmental activist, organising protests across the globe. He was deeply embedded in the protest community: he slept with fellow activists and his longest relationship lasted six years. The spell ended when, in January 2011, Stone was revealed to be Mark Kennedy, an undercover police officer from a unit designed to infiltrate protest groups. Kennedy in his ‘real life’ had a wife and two children; he found it increasingly difficult to make sense of his double existence (one tattoo on his forearm showed skin being pulled back to reveal mechanical levers). The exposure of Stone’s true identity prompted investigations into the wider workings of undercover policing. It’s now known that between 1968 and 2010, at least 144 police officers disguised as activists informed on protest groups.

In her afterword, Clare Clark explains that Kennedy’s story ‘planted the seed of this novel’ in her mind. The book centres on Tess, who as a teenager in the 1990s became active in a climate protest organisation. In this milieu, she fell in love with Dave Taylor, an