The New Avengers (1976)

S1E2 House of Cards

After Steed's plan is disrupted by a group of loud teenagers who save his target, spymaster Perov appears to take his own life. However, just a few days later, his network of sleeper agents, known as the House of Cards, springs into action. This forces Steed, Purdy, and Gambit to confront those they once considered allies in a battle against their own trusted friends.