Ten Days' Wonder by Ellery Queen

In this gripping mystery, a young man named Howard Van Horn suffers from blackouts and seeks the help of his friend, a brilliant detective, to uncover the truth behind his troubling episodes. As they delve into the investigation, they unravel a complex web of deceit, family secrets, and psychological intrigue that challenges their perceptions of reality. With each revelation, the stakes rise, leading to a shocking climax that tests the limits of friendship and trust.