The Enterprise is assigned to take two enemy species, the Anticans and Selayans, to the negotiation table in the hopes that they can join the Federation. If the Bajorans couldn't, then these guys shouldn't. They should be called the Toolboxians and the Lamerons. Someone should lock the doors on their quarters so they can't get out and commit serious crimes like murdering each other and (more importantly) annoying members of the audience.
Really, what do the two alien races have to do with anything here, except as a needless backdrop to frame a story that has nothing to do with them? The real story is about a mysterious energy pattern that starts by zapping Worf before transferring to Crusher and then the Enterprise's computer system. Eventually it kills an engineer named Singh, who would be a red-shirt if not for the fact his uniform is technically gold. Finally, it ends up in the captain, taking control of his mind and body.
The episode, exceptionally nondescript, is a strong argument for making quick analyses of potential threats. To be fair, though, I sort of liked the notion of an investigation that is not pumped up into an overblown drama, and instead shows the workings of a starship and its officers, tackling the subject of what the officers might plan as a contingency if the captain is acting under an alien influence. What's hard to swallow, though, is that the captain could exist as pure energy and survive apart from his body in an energy cloud — but, hey, it's Star Trek. One of the episode's somewhat amusing conceits is Data reading up on Sherlock Holmes and adopting the persona (complete with pipe) in his effort to solve the case. But this case has no legs.