Possible Clues:

• Woman good at breaking into cry of surprise
• Annual award for mystery writers
• Novelist, -- Christie
• Theatric saga I composed, ending of which is kept secret
• Saint whose name means 'good'
• Christie who created Hercule Poirot
• Woman's cry of delight about gun
• She's concealed by a fag at Harrow
• Dame --- Christie
• ...... Christie wrote great detective stories