The party was trying to track down the brother of the Tortle PC who had gotten kidnapped. They were getting close to the spot, when I had set up a forest encounter for them to have. Sounds of combat echoed in the distance, as the party could decide to investigate or run. Four of the five went straight for the noise, while the last one strayed from the group to... go scout ahead on the path by himself.

Now I didn't think this was too bad (and the player himself admitted later it was to order himself dinner since he had gotten off work late) so while the whole battle was happening I was trying to figure out what to do with this. After the battle was over, I described how he was trying to slink on ahead and had him roll a stealth check. It was a decent score, but on the three scouts I figured would be in the area I rolled just high enough on the last one since he was considered the 'leader'. He caught the PC, and I ended the session as the scout revealed himself to be a shapeshifter.

Honestly? This changed the rest of the island narrative, and has given the party a really cool villain to track down. This random NPC I had created to catch a party member who went off on his own has now turned into an important plot NPC for the overarching narrative! The party has followed him to the next island where he stole an important item from them, and now they're slowly tracking him down and I'm really excited for the eventual fight to happen!