Bratva Obsession. Volkov Brothers, #1

He was supposed to silence her. Now he'll kill anyone who tries to take her away. Lena Miller's worst mistake wasn't catching her boyfriend cheating. It was delivering a package to the wrong penthouse at the wrong time. One minute, she's a struggling courier trying to survive another miserable day in the city. The next, she's standing over a dead body with a gun pointed at her by the most dangerous man she's ever seen. Maksim Volkov should kill her.
Instead, the ruthless Bratva enforcer drags her into the shadows of his violent world and keeps her locked away as his prisoner. Maksim says it's temporary. Lena knows better. Men like him don't let people go. Especially not after he touches her. As rival factions close in and betrayal tears through the Bratva, Lena discovers the monster holding her captive may be the only man willing to burn the world to keep her alive.