Despite its simple chemical formula, cupric oxide (CuO) has a surprisingly complex magnetic behaviour which remains only partly understood. Interest in CuO has recently resurfaced with the discovery of a magnetically-induced multiferroic phase at high temperatures. Neutron scattering has revealed that the multiferroicity is accompanied by a change in the magnetic structure from a commensurate antiferromagnet at low T, to an incommensurate helical structure in the multiferroic phase. We have investigated the spin dynamics and magnetoelectric behaviour in CuO, to understand the mechanism that drives the multiferroic phase. We have recently measured the complete spin-wave spectrum throughout the Brillouin zone, but we have found that the data cannot be modelled within the symmetry imposed by the published crystal structure. We therefore wish to use HRPD to determine the structure of CuO.