A recent experiment (RB820171) unexpectedly revealed that a sample of beta-Mo2N exhibited a number of extra reflections at 4 K; a temperature below the superconducting critical temperature of the nitride. We propose an experiment on POLARIS to investigate systematically the evolving structure of beta-Mo2N between 293 & 2 K as the nitride moves from the normal to the superconducting state. Importantly, we propose to perform this experiment as an in-situ resistivity measurement using unique facilities at POLARIS. The structure of beta-Mo2N has never been accurately determined at 293 K and never investigated in the superconducting state (nor at intermediate temperatures). We propose to perform the first in-situ resistivity neutron experiment through a superconducting phase transition and in the process unravel the potentially complex sub-ambient structural phase behaviour of beta-Mo2N.