Margery Allingham 
Look to the Lady [EPUB ebook] 

The Gyrth family had guarded the Gyrth Chalice for hundreds of years. It was held by them for the British Crown. Its antiquity, its beauty, the legends that were connected with it, all combined to make it unique. It was irreplaceable. No thief could hope to dispose of it in the ordinary way. And indeed no ordinary thief would dream of trying. Kept in a windowless chapel, and protected by a fearsome curse, the Chalice should be impervious to thievery.