It's worth noting that this is the second-to-last episode in the season. I am not disappointed.
An old friend of Picard's, Captain Keel, secretly contacts and rendezvous with Captain Picard regarding his suspicions of a conspiracy within the Federation, echoing concerns from an earlier episode, "Coming of Age". Captain Keel informs Picard that affected officials seem not to remember personal historical details, such as whom introduced whom decades ago, etc. However, Keel cannot tell the captain much else, especially after his ship is mysteriously blown to bits. Under Picard's orders, Data finds an unusual pattern of Starfleet orders supporting Keel's suspicions. The bridge crew is informed and the Enterprise returns to headquarters to confront the problem. Upon their arrival, former confidant Admiral Quinn attacks Riker in an attempt to invest Riker with an alien being. Picard discovers that the heads of Starfleet are similarly invested. Riker fools the heads of Starfleet into thinking that he is infested as they are, just long enough to help Picard defeat the aliens and their mother alien. Starfleet is returned to normal.
I am quite delighted that the conspiracy mentioned in an earlier episode has been brought up again and resolved. Continuity between the episodes is nice, even though TNG isn't one of those shows where you have to watch them all and watch them all in order to enjoy them. Still, some continuity helps the show feel like it's going somewhere. Kind of like when Dr. Who keeps seeing weird writing on the wall, and then you finally learn what all that's about. You begin to trust that the writers have a plan for the series and aren't just winging it.
Of course, the special affects are quite laughable by now. If you were watching this with us, you'd hear giggles and shouts referencing everything from Aliens to Animorphs (I'd be the one referencing Animorphs, of course). OMG an alien in my chest! Boooooody snaaaaatchers. Ha ha. I love how the aliens tried to say that they wanted to live in peace and harmony with humans. By taking over their brains. Ha ha ha.
But who wouldn't love watching an old man throw Riker? I'm always cool with Riker getting thrown around.
The best plot point, of course, was when Dr. Crusher tricks everyone into thinking that Riker has been snatched. To make it look like he's been infested, Dr. Crusher attaches a fake protrusion to Riker's neck, imitating the alien's breathing apparatus. Dude, I was fooled. That's one smart lady.