A family of modules with Specht and dual Specht filtrations

We study the permutation module arising from the action of the symmetric group S2n on the conjugacy class of fixed-point-free involutions, defined over an arbitrary field. The indecomposable direct summands of these modules are shown to possess filtrations by Specht modules and also filtrations by dual Specht modules. We see that these provide counterexamples to a conjecture by Hemmer. Twisted permutation modules are also considered, as is an application to the Brauer algebra.