The conversation then went like this:
Rogue: "If he's on the floor now, can I throw it out the window instead?"
Me: "Sure, roll a dex check and see if you make it" [Success] "Yup, the stone flies out the window. The young alchemist screams and runs to look out the little window..."
[Everyone stops speaking and all stare at me to see what they've just done. I let the silence sit for JUST a little while.]
Me: "With another yelp, the young alchemist barrels past you and out the door to get the stone back."
Ranger: "Shit! Quick I'll chase him!"
Wizard: "Me too! After him!"
Rogue: "I'm going to jump out the window."
Everyone shuts up.
Me: "You... what?"
Rogue: "I'm going to use my fancy shoes to jump out the window."
Me: "Ah shit, I gave you magic shoes..."
Bear in mind, with my powers of DM-foresight I knew that there was potentially a big tower battle coming depending on what they did here. I had (wrongly) assumed that they would save the shoes' daily power for a time when they really needed an escape route or something, but no. They just wanted it for badassery. The Fighter and Cleric stay behind to watch over the old guy and then chaos reigned.
Me: "You land gently on the ground and find the jade stone has landed safely in a pile of mud."
Rogue: "Great! I grab it and run! This thing's going back in the sea!"
Me: "Uh... Right."
And here's where all my plans go out the window and we end up in a footrace back down the road towards the beach while I desperately wing EVERYTHING
Forget movement squares, forget the geography, forget how close they all (technically) are to each other. For easiness, I take everyone's relative speed and put them in the order that they left the tower, so:
Tower ---- Wizard - Ranger - Alchemist - Rogue ---- Sea
And for the purposes of fun and speed, everyone can basically keep running or pause to make an attack.
The rogue runs
The alchemist casts some Icy Floor spell at her, but she avoids it and keeps sprinting
The ranger (who's fastest) attempts a tackle, but the Alchemist dodges and keeps running while the Ranger ends up on his face
The wizard and the rogue keep sprinting
The alchemist tries again with a sleep spell which works brilliantly and the rogue is unconscious and down! He grabs the stone and tries to get back to the tower where his master is.
The Ranger is on his feet and decides that his best way to tackle an oncoming runner is with an intimidation check, but he cocks it up.
The wizard asks if he can cast magic missile, and I say yes, but it probably won't stop him...
"What if I rolled a natural 20? Like this one?"
"Then I guess you got him in the leg! He goes down!"
(By now there are six people around the table on their feet, literally yelling at four coins in a line

)
The ranger grapples him to keep him down and the wizard does an arcana check and discovers the nature of the spell that's controlling the alchemist (everyone is now SCREAMING at them to take the bloody stone back!), but fails the check to remove it, the alchemist wriggles free and he's off again. The rogue wakes up and is back in the chase.
The Ranger tries to tackle the guy again, and this time makes the roll so everyone's back down in the mud. No-one takes the stone back yet, but the rogue appears and sits on the guy to make extra-sure he's not getting back up. Finally, the wizard removes the spell and the alchemist stops struggling.
Phew.
He explains that the stone took hold of his master and (presumably) himself sometime after it arrived in the village. They knew it had to go back to the sea, but they also knew they would die if they did that while under its power. He begged the players then to cure his master before throwing the stone away, so the wizard goes back to the town with him, leaving the Rogue and Ranger on the road, holding the stone. Which starts to whisper to them every time they fail a will check

They keep passing it back and forth and getting increasingly edgy until finally the others yell that it's safe and they throw the stone back into the sea, completely avoiding all the battles I had planned by doing something FAR cooler
The next day they head back to Grem's hut and find a little boat has washed ashore containing treasures and some more magic items. The players assume it's a thank-you from the sea creatures and settle in to enjoy a month or two of drinking sailor rum while waiting for a ship to pick them up.
-FIN-