  We analyze the hypermultiplet moduli space describing the universal sector of
type IIA theory compactified on a Calabi-Yau threefold. The classical moduli
space is described in terms of the coset $SU(2,1)/U(2)$. The flux quantization
condition of the antisymmetric tensor field of M-theory implies discrete
identifications for the scalar fields describing this four- dimensional
quaternionic geometry. Non-perturbative corrections of the classical theory are
described in terms of a membrane- fivebrane instanton action which we construct
herein.
