By Luke Mullins

When the mysterious substance reappeared on Thursday, March 3, 2011, Frances Sterling decided something had to be done. Everything had been fine when she'd checked the cat food the previous evening. But by the next afternoon the food was covered in a yellow-and-white crumble, just as it had been nearly every day for weeks. She didn't know what the substance was, but it didn't look right.

Sterling has lived for a decade in the Park Square apartments, a 60-unit building across the street from Meridian Hill Park in DC's Columbia Heights neighborhood. For most of that time, she has cared for two cats—she named them Jolson and Mama—that live outside the building. Several times a day, she has placed dry cat food under the bushes on either side of the building's front door. Jolson would paw at Sterling's first-floor window when he was hungry. "I'm a sucker," says Sterling, who is 46.

In ten years of feeding the cats, she had never seen anything suspicious. Then in February of last year, she discovered several small bowls of what looked like antifreeze near the apartment's entrance. Around the same time, the yellowish-white substance began appearing on the cat food. No matter how often she cleared it away, it always returned.

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