You tell the Primpsk that was stolen to burst into spores/acid/whatever at an appropiate time, ie to infect some of the aliens. You send the diplomatic probe to chase the alien pod, however, the pod had a bit of a large head start, and it reaches the alien mothership first. A couple of minutes later, the mothership disappears.
A bit pissed that you won't be getting faster than light travel any time soon, you begin to 'develop' the Primpsk civilization more. You think about making the Primpsks peaceful, but decide that making them more pragmatic would be more in line with their cultural ideas. After all, these are the species who mangle their own sexual organs to prevent more brood-mothers from appearing.
Surprisingly, less than a day later, the alien mothership appears again, near the Oot cloud. It releases a pod, then disappears again, far too quickly for you to react. You send one of the Primpsk ships over to investigate. Oddly enough, the Primpsk that they stole was inside the pod. You quickly communicate with the Jethro parts.
Obviously, there was no chance to infect one of the aliens. The entire time they were covered with protective gear, either to prevent infection or because they couldn't breathe the same atmosphere, or perhaps both. The aliens, who you will have to name, planted electrodes on the Primpsk. Next, cards were shown, with pictures of colours or shapes on them. This continued for a long time, with the pictures becoming more complex, and involved actions like eating or running or some other easily reconized action. Clearly, the aliens were trying to use the Primpsk's brainwaves to deciper their language.
And it worked. After five or six hours, a robotic voice spoke with terrible Primpskese. A couple more hours pasted, with the voice becoming clearer and clearer, until the aliens were sastified that they understood Primpskese.
Appearently, they will return after around 3 days, to give the Primpsks time to release what actually happened, in the hopes that they will accept the alien's actions, and allow communication between the two species.
Clearly, that's three days to figure out a trap.