A River Called Time: Courttia Newland

A monumental speculative fiction story of love, loyalty, politics and conscience set in parallel Londons
The Ark was built to save the lives of the many, but rapidly became a refuge for the elite, the entrance closed without warning. Years later, Markriss Denny is one of the select few granted entry. He carries with him a closely guarded secret: the ability of his spirit to leave his body and transcend the known world.
But once in, he learns of another who carries the same power, and their existence could spell catastrophe for humanity. Denny is forced into a desperate race to understand his abilities, and in doing so uncovers the truth about the Ark, himself and the people he thought he once knew.