Cloak-and-dagger man is an idiom that refers to a secretive and mysterious person who engages in espionage, subterfuge, or conspiracy. There are many synonyms for this phrase, including spy, undercover agent, secret agent, intelligence officer, black ops operative, and covert operative. Other synonyms might include ninja, assassin, saboteur, or saboteuse. Each of these terms suggests a person who operates in the shadows, using stealth and cunning to achieve their objectives. Whether you're writing a spy thriller or just need to describe a character who operates in secret, these synonyms are a great way to add nuance and intrigue to your writing.