What is locked within is our other selves, our memories of our past lives.
Nathan, the hero of this story, is haunted by dreams in which he half remembers, sometimes fully remembers, dramatic events that occurred during previous lives, but is unaware when the book opens of an organised group called the Reborn who remember clearly, and benefit from the experience gained during, their past lives. These Reborn are in a war against another, very different, group whose aim is to prolong this one life (as they see it) indefinitely, as vampires or whatever, and who will do anything to achieve that goal.
Needless to say, Nathan gets caught up in the battle which takes place in his home-town of New York, a battle which is just one small part of the on-going war between Good and Evil. And like all reluctant heroes, he has to make painful choices regarding his personal life.
Being a great believer in reincarnation, I loved this particular urban fantasy world with its reborns and its horrifying “soul-eaters”, and would welcome a sequel, preferably featuring Nathan and the witch Candace as partners. In Locked Within, Nathan works alone, and I always have difficulty identifying with male protagonists, even one as sympathetic as Nathan, though I must say in this case I was certainly helped by the fact that the earlier self Nathan most closely identifies with is a woman, a warrior named Marjorie. We are even there with him while he as her is being gang-raped – and I mean gang literally: she is captured and raped by a group of ruthless professional thugs.
Candace, who has only a very minor role in this book, but on the other hand is still very much alive, is just my cup of tea.