Books in the Charlie Hardie series

There are some criminals so dangerous the world can never know about them. They can't be held in regular prisons. They must never be released. They're here - in a secret underground prison miles away from anywhere. And now, so is Charlie Hardie. The shadowy organisation running the jail sent him there as punishment for getting in their way. But he's not a prisoner. He's in charge. He can leave any time he wants, he's told. There's just one catch: if he goes, everyone in the prison dies, including innocent guards. But when Charlie realises his family may be in danger, he knows he must protect them at any cost. Even if it means blasting his way out, one inmate at a time...