A dangerously beautiful woman, particularly one who is a fictional character, can be called a femme fatale. A femme fatale usually means trouble for the men who fall for her seductive ways.
Use the noun femme fatale to describe the character in your mystery novel who uses her mysterious beauty to seduce the detective hero into nearly making a terrible mistake. It's a term that has been used in English since the 1880s, and it comes from the French femme, "woman," and the Latin fatale, literally "decreed by fate," but in this case meaning something closer to "disastrous." Famous literary femmes fatales include Medea and Catwoman.