Several rotational levels in the lowest excited bending state of HeHCN have been observed at hyperfine resolution by electric resonance spectroscopy near 100 GHz. The observed transitions correlate to the j = 1 <-- 0 transition in the limit of free internal rotation. The ground state has been characterized by using millimeter wave/microwave double resonance. One-photon transitions in the ground state are not observable using electric resonance, due to poor focusing of the nominally j = 0 levels. Ground-state J = 1 <-- 0 and J = 2 <-- 1 transitions were measured at 15893.6108(41) and 31325.2443(82) MHz, respectively. Quadrupole coupling constants eq(J)Q were determined to be 0.1118(15) MHz for J = 1 and 0.199(12) MHz for J = 2. We have calculated rovibrational energies and wave functions arising from an ab initio intermolecular potential, calculated at the MP4 level using a large basis set containing bond functions. The potential is characterized by a well depth of 25 cm(-1) at the centers of mass separation R = 4.27 Angstrom. The global minimum occurs at the collinear He-H-C-N configuration, and the minimum energy rises monotonically, with large angular-radial coupling, as the HCN orientation angle theta increases from 0 to pi. Calculated and observed transition frequencies, including hyperfine structure, agree to within 10%. We have used the calculated Coriolis interaction energy to deperturb the measured ground-state spectroscopic constants. This procedure permits estimates of vibrationally averaged structural parameters. We find, for the ground state, [R(-2)](-1/2) = 4.23 Angstrom. Very large amplitude radial motion results from zero-point energy that is 75% of the 25-cm(-1) well depth. The hyperfine data reflect very weak anisotropy in the potential, with [P-2(cos theta)] = 0.092 (J = 1) and [P-2(cos theta)] = 0.115 (J = 2). These values are very close to [P-2(cos theta)] = 0, characteristic of a free internal rotor. The centrifugal distortion of eq(J)Q indicates that, as in the other rare gas-HCN complexes, significant angular-radial coupling causes the HCN to align with the intermolecular axis in the rotating complex.