From End of Casefile #12: Beautiful young heiress Tessa Carpenter thinks she needs protection, and the Hardy brothers are the ones to provide it. She has just forced the Bayport Museum to return her family's art collection to her -- a collection that includes the infamous Borgia Dagger. Legend says that if its owner touches the dagger, he (or she) will die within weeks. Tessa has touched the dagger, and now she's become the target of many dangerous accidents. But there is more menace in Tessa's life. A disgruntled former servant has been threatening her; an old family friend nearly poisons her; even Tessa's boyfriend may not have her best interests at heart. Frank and Joe must discover the true secret of the ancient treasure -- before it's too late for them all.

From back of book: Beautiful, rich, and very spoiled, Tessa Carpenter is all trouble from the moment she sideswipes Callie Shaw's car -- and meets Frank Hardy. She invites Frank and Joe to a party for a close-up look at her priceless treasure, the Borgia dagger. But in the middle of the party the lights go out and Tessa is almost killed. Fearing the ancient curse on the jeweled dagger, Tessa asks the brother detectives to protect her. The question is -- will two bodyguards be enough for someone with enemies on both sides of the grave?