In 1955, small-town police chief Art Moran is thrown into a world of danger and mystery when he is tasked with solving a gruesome murder in an isolated mountain cult. Despite feeling out of his depth, he becomes the only person the cult members trust. But things take a turn for the worse when, in a single night, Art loses everything he holds dear, including his love, his son, and even his sanity.

Forty years later, the ghosts of the past come back to haunt him as he is called upon to solve the murder once again. As he delves deeper into the mystery, he finds himself questioning everything he thought he knew about redemption, forgiveness, and love. Set in the backdrop of a small town in upstate New York, Diamond City also explores the complexities of small-town life, including its subtle racism and pettiness. But through it all, Art learns that it's never too late to embrace the life he has been given and let go of his impossible dreams. Will he survive the challenges that come his way and find the redemption he so desperately seeks?