Zero 22 / Chris Ryan.

"The SAS is operating covertly in the wartorn badlands of northern Syria. They know it will be gritty, bloody and dangerous. But when Regiment legend Danny Black's unit, codenamed Zero 22, is tasked with a more routine operation, they don't expect it to end the way it does: in compromise and massacre, orchestrated by the shadowy Wagner Group, a paramilitary organisation in thrall to the Russian president. Back in the UK, Danny learns that his unit was betrayed by a mole feeding high-level military intelligence to the Russians. Like any SAS man worthy of the name, his first thought is to avenge the men who lost their lives on the Zero 22 op. He has no hesitation in accepting the mission to assassinate the man responsible for the death of his mates."--Publisher description.