This is actually a very valid criticism that I somehow completely overlooked when writing/designing this little encounter (what I get for not playtesting!). I think the quick fix solution here would be to have the corpses in room 4 be beastmen, one of which has the alchemy book. That way it's a little harder to just pop in and out in the first "room".
In general I think while the overall interactivity of this "adventure" is pretty good, I think it could be improved a lot with regards to scale and overall flow. Things to think about for my next (if I write one?) adventure!
Thanks for the feedback!