The Infectious Madness of Doctor Dekker is a unique Lovecraftian FMV (full-motion video) murder mystery game that allows players to type their own questions instead of picking them from a predetermined list. As a psychiatrist, you are trying to solve a murder while treating the unusual patients of the recently deceased Doctor Dekker. The game features over 1600 full-screen HD video responses and a free text input system that allows players to ask whatever they want, including questions, phrases, or just keywords.

Additionally, the game has multiple endings, multiple stories, and six main suspects and five side-quests, including John Guilor (Contradiction). To combat spoilers, the game has a random murderer chosen at the start of the game. The UI is simple, and players can view evidence, make notes, watch replays, and see their question history. The game also has Steam achievements and a dynamic descriptive rating system. However, be warned that the game contains mature themes and psychological horror, including sexual themes, violence, and suicide, and is recommended for adults only.