Let . C be a fusion category which is an extension of a fusion category . D by a finite group . G. We classify module categories over . C in terms of module categories over . D and the extension data (. c, . M, α) of . C. We also describe functor categories over . C (and in particular the dual categories of . C). We use this in order to classify module categories over the Tambara Yamagami fusion categories, and their duals.