A planet where the Enterprise-D had just finished eradicating an outbreak of Phyrox plague in 2366 when Captain Picard was abducted from his quarters.
Cor Caroli V is a planet mentioned in the Next Generation episode Allegiance.
As the episode opens the Enterprise-D has completed a mission there, wiping out an epidemic of Phyrox plague. Picard notes in his log that the crew are tired and that the ship is on its way to a rendezvous with the USS Hood.
That night an alien probe replaces the captain with a double. The duplicate soon behaves oddly, ordering the ship to a nearby pulsar instead of the rendezvous, while the real Picard is held with three other captives in an experiment on authority.