2:19pm, Moscow time, 16 February 2024. The Federal Penitentiary Service of the Yamalo-Nenets Autonomous District announces that Alexei Navalny is dead. The news sends shockwaves around the world.

In Murder in the Gulag, award-winning journalist John Sweeney goes behind the headlines to reveal what really happened to the Russian opposition leader in the freezing Polar Wolf penal colony in a remote part of Siberia. The book is less a whodunnit - Russian President Vladimir Putin's machinery of repression killed Navalny - than a howdunnit.

The narrative relates Navalny's extraordinary life story in technicolour detail, from his childhood summers spent with his grandparents in the shadow of the Chernobyl nuclear plant in Ukraine to his untimely death at the age of 47, cut down in his prime.

This is a warts-and-all portrayal of a highly charismatic but controversial figure who flirted with far-right Russian nationalists before course-correcting, told by an intrepid journalist, based in London and Kyiv, who knew Navalny personally.

Murder in the Gulag contains a warning. Navalny made a fatal misjudgement in returning to Russia after his poisoning by Novichok in 2020, betting that Vladimir Putin wouldn't kill him. But as Putin has gained in strength, with the death of Wagner leader Yevgeny Prigozhin and the fortunes of war slowly turning in Russia's favour, Navalny lost that bet. Sweeney argues that if the West fails to stand up more forcefully to Putin, we are in danger not just of betraying Ukraine but our own security too.