The starship beams four of the passengers on board, along with the ship's cargo. Two of the guests are from the technically advanced planet of Ornara, and the other two are from its neighboring planet of Brekka. The crew is puzzled when the two groups immediately begin to argue over the cargo.
Picard learns that the precious cargo is in fact a remedy for a plague which has gripped Ornara for two centuries. The "cure" is manufactured exclusively on Brekka, whose citizens provide it to the Ornarans in exchange for food and other basic necessities. However, in this instance, the Brekkians claim the Ornarans did not pay for their cargo, and they prepare to take it back to Brekka.
Pleading that their civilization will be wiped out without the medication, the Ornarans convince Picard to mediate. However, Picard is able only to convince the Brekkians to give doses to the two Ornarans on the Enterprise. But as the Ornarans take the remedy, Dr. Crusher realizes that the alleged cure is nothing more than a narcotic ... and that the Ornarans are a race of drug addicts!
Apparently, the Brekkians have neglected to inform the Ornarans that the plague is not fatal and have instead allowed the Ornarans to become addicted to a bogus cure.
Picard, citing the Prime Directive, refuses to inform the Ornarans that the Brekkians have been deceiving them for 200 years. Instead, he cleverly turns the tables on the Brekkians by withdrawing an earlier offer to repair the Ornaran freighter ship. In this way, the Ornarans will be unable to honor their trade agreement and will consequently escape their addiction.