Tank Squadron X of the Isdenica Rebel Alliance has been defeated after an unsuccessful siege of the Isdenica capitol, and forced to retreat. The only issue remaining, however, is that the trusty squad canine Phos has been missing since the siege first began and has not been seen since.
The rebellion will surely falter if they lose both the battle and their renowned mascot, so the squad has called upon the Enclave to find and recover him. That is your party's goal.
Alternatively, the squad also gives the party the option of kickstarting the siege and finding a way for the rebels to claim some sort of victory as a means of mission success. If they can bring back some good news it will lessen the blow of losing their companion.