  The vector and scalar form factors relevant to the second-class current
$\tau^-\to\pi^-\eta^{(\prime)}\nu_\tau$ processes are evaluated supplementing
Chiral Perturbation Theory with the inclusion of resonances as explicit degrees
of freedom. While the vector contribution is essentially fixed from knowledge
of the two-pion vector form factor, the scalar form factor demands a coupled
channel dispersive analysis to obtain robust predictions for the detection of
these decay modes.
