SHEFFIELD, England — The three men in the street outside her house were there to take down one of the trees she loves, but Sue Unwin nevertheless offered them refreshments — two teas and an orange drink. She did so, she said, with an eye to buying time until fellow tree lovers could get there to help her stop the felling.

The plan worked, at least for that day. Ms. Unwin, an architect, said she thought nothing more about it until a couple of months later, when the police showed up on her doorstep asking questions about what exactly was in those drinks.

Sheffield’s streets are lined with around 36,000 lime, elm and cherry trees, some showering its sidewalks with pink blossoms. The city’s plans to fell 6,000 of the trees during a five-year period had already prompted years of protests and confrontations, pitted neighbor against neighbor, and prompted one octogenarian couple to say they would risk prison to protect the trees on their street.

But matters reached a climax of sorts with the case of the toxic tea, or “Teagate,” as it has come to be known, in which Ms. Unwin was questioned about whether the drinks might have been spiked with a laxative.