"On the inside" typically refers to a person or group being a part of a particular organization, group, or situation, often with an intimate understanding of its workings or secrets. In the context of where spies work, "on the inside" likely refers to spies working within an organization or group to gather information or carry out covert activities while remaining undetected.
Note: The provided meaning of the answer is for the latest New York Times crossword puzzle clue: Where spies work. Explanations are generated by AI and may be inaccurate.