  We enumerate the conditions necessary for $CP$ violation to be manifest in
$n$-$\bar n$ oscillations, and build a simple model that can give rise to such
effects. We discuss a possible connection between neutron oscillations and dark
matter, provided the mass of the latter lies between $m_p-m_e$ and $m_p+m_e$.
We apply our results to a possible baryogenesis scenario involving $CP$
violation in the oscillations of the $\Xi^0$.
