Nope, the treasure chest is locked

[Originally by Phantom Pen]

The treasure chest was still right where Mackenzie left it, as she figured it would be. The chest was large and looked heavy, so the waves weren't likely to be carrying it away any time soon. All Mackenzie would have to do to get her bikini back was pop the lid open and grab the garments. Mackenzie paddled up, set her feet on the sand below, reached down to grab the lid, and pulled.

The lid didn't budge.

Mackenzie's heart skipped a beat. She tried pulling again, but the chest stayed shut. It had opened so easily before! What was going on?! What was different this time? Mackenzie scoured her mind, remembering everything she could about the chest when she hid her bikini inside it. She found the chest, pulled it open, found someone had cleaned it out before her...

But they didn't close it all the way after emptying it! The chest had been open just a crack when Mackenzie had found it, but when she closed it to keep her things safe, she pressed the lid down all the way, and she must have activated the lock in doing so! This was bad. Very bad.

A chill ran up Mackenzie's spine despite the warm water. There had to be some way to fix this. The chest must have been weakened from sitting in salt water for so long, maybe the lock was brittle? Mackenzie planted her feet again, readied herself, and pulled with all her might.

Mackenzie wasn't sure how long she pulled before-