The Wages of Butter
It was a surprise to the nations of Earth to discover that the substance known as ‘butter’ turned out to be an almost perfect stimulant/dietary supplement for the alien species known as the Monisan. One standard stick (cow’s milk butter is the best for the Monisans’ purposes) could keep a single Monisan swarm-soldier going at 120% alertness and reflexes for two days straight, with no psychological or physical side-effects (as long as the Monisan didn’t go out and immediately eat another stick of butter). Since the Monisan Empire consists of roughly eight hundred worlds, with one or two being added via conquest every decade, this surprise was not entirely welcome.
Fortunately for Earth, the Monisan consider our planet to be highly radioactive, horribly bright, and dangerously variable in its mean temperature. They are reflexively reluctant to conquer us outright, which cleared a path for trading for our butter at a reasonable price (‘reasonable’ at first being as defined by them). There was some resistance to selling combat drugs to an aggressive race of sapients, but eventually Earth gave in. The alternative was… unpleasant.
Also, it cannot be denied that the arrangement has been mutually beneficial. Every remaining nation-state on the planet is heavily involved in butter production; even so, the demand is so high that most humans use non-cow’s milk butter now. There’s always a shipment being picked up for offplanet distribution, which has triggered a dramatic rise in our space infrastructure. For that matter, the money and military surplus the Monisan give us for our butter (to say nothing of our ongoing relationship with them) has made Earth rich and secure in a slightly dangerous galaxy. There is a vested interest in maintaining that state of affairs. There are many vested interests. Butter is now an extremely valuable substance, in other words.
Which leads to the current problem. There’s a briefcase full of butter samples that has gone AWOL. It was supposed to go to a Monisan facilitator for analysis and assay, but elements of our organized crime network stole it instead. It is believed that they plan to sell it to elements of the Monisan organized crime network, presumably as a combat drug. The Monisan are no more (or less) willing to tolerate criminal behavior than Earth is, and this heist was particularly brazen. Track down the briefcase, secure the samples, bring in whoever you can for arrest.
Also: ignore any rumors or protestations that the butter is actually going to go to Monisan revolutionary groups, as part of their ongoing rebellion against the Monisan Empire. For one thing, they’re probably lying. For another, the Monisan revolutionaries are even worse than the Monisan Empire. Interstellar combat drug smuggling is hardly the worse thing they’ve ever done.