The doors at least do not seem to be illusory. Nor do they seem locked. Henri opens them and is greeted by two fishmen on your left looking at him, then looking expectantly at the ceiling where what appears to be two automatic fully-steerable clockwork crossbows are located. The crossbows are pointed at the entrance (which is to say, at you), but do not seem to do anything at the moment.

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Fishmen init: (1d20+1)[7] (everyone roll your init, but you still get to act now, even if it is lower than 7)

=> Party