The group presses on, taking the north-facing hallway. The hallway continues for sixty feet before it reaches a small set of stairs climbing up to a wooden door. Boide pushes the door open and reveals a 30 foot wide, by 20 foot long room. Along the north wall of the room stand five flesh golems. Each has a number branded onto its chest: "5, 7, 9, 11 and 13". Behind them, directly opposite the door you entered from, is a wooden door. The one on the left, the golem wearing the number "5", says "One of us does not belong with the others. If you can pick it out, it will serve you and the others will allow you passage. If you pick the wrong one we kill you. You have 60 seconds."
Alas, this kind of puzzle works best in a face to face game. The adventure tells me to start a timer immediately set to 60 seconds to put real time pressure on the group. That's not reasonable in this format - so I'll compromise, you have 2 hours. It's 11:30am where I am, if you haven't posted an answer by 1:30pm, the golems attack. The first answer posted is the answer that will be taken - if it's wrong, the golems attack.