The diffuse neutron scattering function S(Q, omega ) from a single crystal of deuterated adamantane in its 300K plastic phase has been measured throughout the 110 plane of the reciprocal lattice, and over the range of energy transfers h(cross) omega up to 12 meV in which intermolecular vibrations occur. The results are presented as contour maps of S(Q, omega ) over the reciprocal zone at fixed energies. They reveal the translational and librational phonon modes which have been intensively studied to be a minor feature of the scattering at energy transfers above a few meV. The underlying reciprocal lattice structure is soon lost, and the scattering is dominated by a smoothly varying dynamic structure factor. At the higher energies this becomes increasingly isotropic in scattering vector with liquid-like oscillations in Q and a major peak at 35 nm-1.