Deadlock (Ryan Lock 02) by Sean Black

"The California State Prison at Pelican Bay holds three and a half thousand of America's most violent criminals. Three thousand, four hundred and ninety nine of them want the remaining inmate dead. Your job is to keep him alive until he testifies..."
The second novel in the Ryan Lock series, Deadlock is an explosive, race-against-time thriller for fans of Lee Child, Robert Crais and James Patterson.
Elite bodyguard Ryan Lock has become a convicted felon, sentenced to twenty years in Pelican Bay, California's notorious Supermax prison. Or at least that's what the United States Justice Department wants everyone to believe.
In reality, he's there to protect one man. Frank 'Reaper' Hays, a founding member of the white supremacist Aryan Brotherhood, is about to give evidence against members of his own gang for the brutal slaying of an undercover ATF agent and his family.
And just to make an already difficult job next to impossible, Reaper refuses to go into protective custody. In a world dominated by violent men, where alliances are constantly shifting and no one can be trusted, Lock knows that he faces the toughest assignment of his career – just to stay alive..