Palmyra II was a planet. In the 23rd century, its planetary ruler gambled away his fortune in a casino on Rigel II. The owner, an ex-Orion slave girl named Marta, married him and took the planet for herself. To dismantle the world's corrupt bureaucracy, Marta famously invited the worst offenders to a private dinner and performance of Macbeth and poisoned the wine. (Decipher RPG module: Narrator's Guide)

Palmyra II was presumably liberated when Marta was captured by Starfleet and imprisoned on Elba II.