The quarry heads off into the wilderness! Play out a Journey as usual, but use Tracking instead of Navigation. Time is obviously critical. Every time the PCs manage to shave a unit of time off the trip, roll 3d. Modifiers: +Peril; +1 for every unit of time the PCs have lost; -1 for every unit of time they have gained. On an 8 or less, they catch their quarry.
Ultimately there are three alternatives here. (1) The PCs catch up. The two groups will then meet and resolve things, one way or another. (2) The PCs don’t catch up, but do manage to track their quarry to the adventure site. Then they’ll have to complete the adventure in order to find their quarry, who is at the Goal! (3) The PCs get a critical failure while tracking and lose the trail. Then they’ve lost their quarry, and this adventure is over.