Star Trek: 25 Greatest Next Generation Episodes
13. The Pegasus
In what, for God only knows why, served as an eventual crossover with the finale of Enterprise (thanks a lot, Berman), Riker's first captain, now Admiral Eric Pressman (played by Terry O'Quinn of "Lost" fame), comes aboard and places the Enterprise on special assignment: to find his and Riker's lost ship, the Pegasus, presumed destroyed twelve years ago in a warp core breach. So why the big hoopla about a crappy lost science ship? The Romulans are looking for it as well for some odd reason.
A big Riker episode, we learn more about what happened on board the ship the day she blew: mutiny aboard a Federation starship over whatever it was they were doing and Riker, fresh out of the Academy, defended Pressman when the crew pulled phasers on him. The mutineers went down with the ship, and the whole thing was covered up by Starfleet.
Why? Because of the exact same reason the ship is found encompassed in solid rock in an asteroid field... a Federation cloaking device.