400 Days is a gripping blend of mystery, suspense, and emotional drama that follows Keshav and Saurabh as they investigate the disappearance of a young girl named Siya. When her desperate mother approaches Keshav for help, he becomes deeply involved in a case full of secrets, lies, and unexpected twists. As the investigation unfolds, Keshav must confront his own personal dilemmas while navigating a world where nothing is as it seems. Chetan Bhagat weaves a fast-paced narrative filled with intrigue, romance, and moral conflict. 400 Days keeps readers hooked with its relatable characters, sharp dialogue, and a mystery that reveals the complexities of modern relationships.