  We show that any eight-dimensional oriented manifold $M$ possessing smooth
circle action with exactly three fixed points has the same weight system as
some circle action on $\mathbb HP^2$. It follows that Pontryagin numbers and
equivariant cohomology of $M$ coincide to that of $\mathbb HP^2$; if $M$ admits
cellular decomposition of only three cells, it is diffeomorphic to $\mathbb
HP^2$.
