Nematic liquid-crystal wetting at a solid interface presents particularly interesting features when the nematic director orientation at the solid interface is antagonistic to that favoured by the emerging nematic - isotropic interface. We have used the Landau - de Gennes theory of an inhomogeneous liquid crystal to make a quantitative study of this phenomenon, for the case when the solid surface favours homeotropic anchoring but the nematic - isotropic surface favours planar anchoring. By generalizing the theory of Sheng to allow spatial variation of the director, we find a richer surface phase diagram exhibiting a prewetting line or boundary transition shifted from that discussed by Sheng, as well as a transition between two nematic wetting phases, at which the wetting layer director profile changes from a homeotropic to a distorted texture.