Since I don't have more information about this 'all in the mind novel', it could be a story that delves into the inner workings of the human mind. It might tell the tale of a person who discovers that everything they thought was real was actually a construct of their mind. It could also be about the battle between rational and irrational thoughts within a character's head, and how that affects their relationships and life choices.
The 'all in the mind novel' might revolve around characters whose lives are deeply influenced by their mental states. Maybe it shows how their thoughts, fears, and desires shape their reality. It could explore themes such as mental illness, the power of positive thinking, or how the mind can create its own prison or paradise.