  We formulate the generic $\tau$-function of the Painlev\'e II equation as a
Fredholm determinant of an integrable (Its-Izergin-Korepin-Slavnov) operator.
The $\tau$-function depends on the isomonodromic time $t$ and two Stokes'
parameters, and the vanishing locus of the $\tau$-function, called the
Malgrange divisor is determined by the zeros of the Fredholm determinant.
