The Infectious Madness of Doctor Dekker is a mystery video game in which players assume the role of a psychiatrist trying to solve the mysterious murder of Dr. Dekker. The player must interview and treat the strange patients left behind by Dr. Dekker as they search for clues about who committed the crime, gathering evidence along the way. The murderer's identity is randomly generated, so players must use their wits and deduction skills to uncover it while also attempting to unravel the chaotic web of secrets left behind by Dr. Dekker before his death.