Firewall by Andy McNab

Tough, resourceful and ruthless, ex-SAS trooper Nick Stone is now working for British Intelligence on deniable operations. And is desperately in need of cash. When he is offered a lucrative freelance job, Stone thinks his problems are over. All he needs to do is kidnap a Russian mafia warlord. And so Stone is thrust into the grim underworld of Estonia, with unknown aggressors stalking the Arctic landscape. Russia has launched a cyber-espionage attack, hacking into the West’s most sensitive military secrets. Stone must stop them. But the mafia are waiting in the wings with their own chillingly brutal solution…