User blog comment:Creeper50/Fighting Back: A Short Video Game by Luca/@comment-6548012-20151206010319/@comment-26399604-20151209160034

If you made it apparent in the story that the doctor's assistance with his patient was a last resort, then I think it would help justify it. You could also establish that the doctor and the patient are or will become close friends prior to the events. This would provide more motivation to help his patient. Moreover, if as FrenchTouch said, Exorcists are few in number -- this might be another reason for the doctor's intervention with the absence of any external help.

If all else fails, you can still use all the listed a reasons above but just have the doctor not believe in the demon aspect, but his skepticism is tested based on the "strange" events happening around his patient. It's up to you where you want to go with it, but I think you could make a believable game with a few tweaks to the storyline (or bits you will uncover later as you play).

Overall, it sounds like an interesting game to play. Alternative endings are always a cool aspect to a game and it adds to its replay value. Hope it turns out well!