A world in political collapse where Riker was captured during an undercover mission to rescue a Federation research team.
Tilonus IV is a planet whose government has collapsed into instability. The Federation has a research team on the surface, and Starfleet sends Riker in disguise to extract them.
In Frame of Mind, Riker is captured on Tilonus IV and subjected to a neural extraction device. His mind constructs a confusing blend of an asylum and his rehearsals of a play aboard the Enterprise, until he finally breaks through the illusion and escapes his captors.