Double agent noun – A spy who works for two mutually antagonistic countries. Secret agent and double agent are semantically related In some cases you can use "Secret agent" instead a noun phrase "Double agent".
Secret agent noun – A person secretly employed in espionage for a government. Double agent and secret agent are semantically related in spy topic. You can use "Double agent" instead a noun phrase "Secret agent".
Amber Heard plays Blanca Vasquez, a blonde-haired, green-eyed and light-skinned secret agent who claims to be Mexican-American and whose name means "white." She turns out to be a double agent, so maybe she wasn't really latina after all.