  This paper is a sequel to \cite{C}, in which the author studies secant planes
to linear series on a curve that is general in moduli. In that paper, the
author proves that a general curve has no linear series with exceptional secant
planes, in a very precise sense. Consequently, it makes sense to study
effective divisors on $\ov{\mc{M}}_g$ associated to curves equipped with
secant-exceptional linear series. Here we describe a strategy for computing the
classes of those divisors. We pay special attention to the extremal case of
$(2d-1)$-dimensional series with $d$-secant $(d-2)$-planes, which appears in
the study of Hilbert schemes of points on surfaces. In that case, modulo a
combinatorial conjecture, we obtain hypergeometric expressions for tautological
coefficients that enable us to deduce the asymptotics in $d$ of our divisors'
virtual slopes.
