Dr. Fausto, a surgeon who deals with terminally ill cases, is on his way to a medical convention where he is due to present a paper. On the way he is accosted by the devilish looking Santos Vela, a man who claims the doctor operated on him years ago. This is not a chance encounter. "Vela" follows the good doctor about, offering him happiness and the fulfillment of all his wishes, good and bad. And in spite of himself, Dr. Fausto succumbs.
Of course, getting your wishes fulfilled isn't always a good thing. Pretty soon, Fausto realizes he is in over his head. Things are getting--to say the least--creepy. How will he ever get out? How will he ever get rid of the Mephistophelean Santos Vela? Or, will he?