Secret of the Laurel Crown

The note on the old shoebox read: "Carolyn, I bought this at a garage sale. I know how tough life has been for you these past months. I thought this might help a sad girl smile. Love, Gram."
Carolyn lifted the lid and dumped its contents. Five hundred pieces of the jigsaw puzzle tumbled out onto the worn yellow wool blanket. As she pushed the pieces aside, a folded parchment-its edges ragged with age-caught in a small hole.

Picking it up carefully so as not to tear the creases, she unfolded it and read the words in faded black, handwritten script: "he agape nikai panta. The Laurel Crown shall choose the wearer. Be warned. Beware of the Baal Contract."

Was the secret message about the puzzle? Maybe the message had nothing to do with the puzzle. Somebody from a foreign country could've put it into the box later on. But why? And who?
In seeking answers to those questions, Carolyn and her brother Jimmy's adventures begin on the planet of Double Suns.