One Tuesday, a sharp-elbowed man in a pinstripe suit shoved past her for the last remaining seat. Eleanor didn't flinch. She just smiled, revealing a row of even, pearl-white dentures. "That's a lovely briefcase," she said, her voice a dry rustle. "Does it contain your integrity?"

Eleanor sighed. Kids today have no finesse.

Tomorrow, she'd ride the District Line. There was a corrupt MP who needed a gentle reminder on the Circle Line, and she knew exactly where his panic button was located.

They were wrong.

At King’s Cross, Eleanor didn't get off. She never did on Tuesdays. Instead, she shuffled to the end of the carriage, where a nervous young woman was surreptitiously taking photos of a sleeping drunk’s wallet slipping from his pocket. Eleanor sat down heavily next to the woman.

To the commuters, she was simply "Tube Granny"—a stooped figure in a tweed coat and a felt hat, a human seat-filler between their earbuds and their phones. They saw her wrinkles and assumed she was fragile. They saw her age and assumed she was invisible.

She waited. At Warren Street, her real target boarded. He was a smug-faced art dealer known for fencing stolen antiquities. The police couldn't touch him. But Eleanor could. As the train lurched, she "accidentally" stumbled, her cane hooking his ankle. He grabbed the rail, dropping his designer messenger bag. In the chaos of apologies and "oh dears," Eleanor’s gnarled, swift fingers palmed a small, wax-sealed envelope from a secret pocket inside the bag. Inside was the provenance of a stolen Benin Bronze.