Oh, hasn’t Picard learned? You don’t just let some stranger futz with your ship’s computers. It’s not a good idea. It wasn’t a good idea back in the day either. I’d say the Enterprise is doing well enough, thanks, and any “mainframe upgrades” are unnecessary.
Anyway, these pesky little guys who look like mini-Talosians fake the crew into thinking the ship is about to explode. Everyone flees to the Starbase (except Yar and Worf who are already there, obviously playing games from Tron since they are wearing bright blue spandex) but Riker and Picard are “held” at the pesky Holodeck by a rather alluring program. Perhaps TOO alluring!!! Eventually things are revealed as not quite so evil as they first seem and a deal is worked out.
I’m not exactly fond of any episode involving the Holodeck, but in all this is a good one. Maybe I give it four insignia merely because in comparison to the other horrid episodes this one seems really good. Anyway, I won’t question it too much — it is enjoyable.