Witcher 3 — Possession quest ending

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I'm a little confused about one of the possible conclusions of the side quest "Possession":

In the "Trick" ending, Cerys gives Geralt a the baby, and tells him to put the baby in the oven. If the player obeys Cerys, Geralt puts the baby in the oven(!) and slams the oven door shut, then puts a Quen barrier around it. It's later revealed that the baby is completely unharmed, and in the adjacent room.

My question is, how is that ending possible?

Geralt is the one who started the fire, and had to truly believe that he killed the baby in order for the trick to work. How did the baby get from the oven, to the adjacent room? How did the other character (a priest, I believe; I don't remember his name) arrive in the house, get to the adjacent room, and retrieve the baby while everyone was fighting and a Quen barrier was around the oven?

I expected that Cerys would explain things afterward, but I didn't have any option to discuss it with her. Is this explained or hinted at elsewhere in the game?

Best Answer

If you take your time to explore the house before hand (as I did even before getting the quest and it scared the shit out of me with the sounds it made) you could find a room behind the oven.

If you go into this room behind the oven you can see it has an opening on that side too. The old dude (whose Name is Hjort :) ) who walks out with the baby was waiting in that room and knew Cerys plan. Therefore tricking Geralt into thinking he was responsible for killing the baby tricking the Hym.