Sting

Never do a favor for a friend.
Twelve-year-old March McQuin forgot rule number one for cat burglars, which is how he and his twin sister, Jules, found themselves dangling upside down twenty feet above a stone floor at three in the morning. Their target was a set of stunning diamonds and it should have been an easy job, in and out. Except another thief got there first. March and Jules were lucky to escape with their lives, and one measly stone.
Now the botched heist has created a world of trouble. The stone they grabbed was the Morning Star, one of a trio of famous sapphires, and it's cursed. The theft put the twins and their friends in the crosshairs of Interpol, the FBI, and a vicious adult gang of international criminals. And worst of all, the only way to break the curse and set everything to rights is by somehow managing to steal the other two sapphires in the set.
Break out the black gloves. Lay out the masks. There's a full moon coming, and jewels to steal...