3. When he saved an entire mall from an anthrax attack
Gideon, Reid, and Prentiss traveled to Guantanamo Bay to interrogate a terrorist who was leading a sleeper cell from the inside of prison. The terrorist had been detained when his home was raided and the authorities found a chemical weapons dispersal device. Through conversations and psychological tactics, Gideon was able to determine the planned attack—the grand opening of one of America's largest malls. True to form, SSA Derek Morgan took down the terrorists just moments before they were able to release the chemicals into air vents.
Season 2 Episode 10 "Lessons Learned"