Shelley King said 13-year-old Archie was tied to a railing Monday outside a Marks & Spencer store while she shopped, and he was gone when she went out to get him, The Daily Telegraph reported Friday.
Archie is the inspiration for Sita Brahmachari's 2011 Waterstones' Children's Book Award winner,
"I felt awful. It was my worst nightmare because I don't usually leave Archie outside," King said. "My partner or I usually stand with him but it was just a quick thing. I'd just picked him up from the dog sitter and we'd been for a walk on Hampstead Heath and I thought, 'You're being stupid, there are other dogs out here.' It's the worst thing."
King said Archie has a slipped disc in his back and requires medication.
"You can't just steal a 13-year-old dog, it's a responsibility to have an old dog. Archie's a real terrier -- he's got a strong will and personality," King said.
King put up posters in the area and police were investigating the theft.