Sand slides off the bottle when you pick it up. There's a tingling sensation in your fingers that doesn't come from the last grains of sand clinging to the glass.
A furtive glance at the other beach-goers assures you that no one's noticed your actions. Good. This is your discovery and you don't want to share it with anyone just yet.
You pop open the waterproof cap and pull out the paper. Its sun-faded and unrolls easily.
The page is blank. (supernatural adventure)
Send help. (mystery)
Please forgive me my dearest. (tine-travel romance)