The cabin is on the shoreline of a dark, murky lake. There was a crude sign on the banks warning you not to go swimming or wading in it. It didn't look all that inviting anyway.
Evening comes as you finish unpacking. "It's a clear moonlit night, why don't we take a walk around the lake? suggests Lisa "The sign didn't forbid that."
You agree and the both of you lock the cabin up and set off. In the full moonlight there is a mist rising from the lake, making it look mysterious.
The full moon also illuminates something else resting on the bottom of the lake, a few feet from the banks. Something shiny.
"What's that?" asks Lisa, pointing to it.
"I don't know. Looks like it's a gem or precious metal."
"Ooh, you have to get it!" said Lisa with excitement "It could be priceless treasure!"
"But the sign said.."
"We're not going far in. Either you get it or I will."