Trey spotted the rest of the group as they were headed back to the place where they encountered the troll. Robert was carrying the egg, which meant that he was able to catch up to the thief.
"I see you got the egg." Trey said, landing nearby. "The mother's probably worried sick at this point."
All they had to do now was find the mother and return the egg, which shouldn't be too hard. Not anywhere near as hard as finding the egg, at least.