In the novel Cat Among the Pigeons, Miss “Chaddy” Chadwick was a senior teacher at Meadowbank School for Girls, a school she had helped Honoria Bulstrode to found. She has spent her whole life thinking about the school hoping to become the new headmistress. Miss Chadwick is a Mathematics teacher in Meadowbank, who has been at the school since the start. She and Elspeth Johnson discover the body of Grace Springer in the Sport's Pavilion.
When Miss Bulstrode announced that she was retiring and everyone suggests that Miss Vansittart will replace her as headmistress, she becomes very upset by the idea. However that Miss Chadwick was heard screaming in the Sport's Pavilion, she had found Miss Vansittart dead bludgeoned by a sand bag.
Miss Chadwick later dies while protecting Miss Bulstrode and Mrs Upjohn from being shot by Ann Shapland. As Shapland had an alibi when Miss Vansittart was murdered, Chadwick confesses with her last words and reveals the truth. Since she was considered to be too old to replace Bulstrode, she had become jealous of Eleanor who she found in the Pavilion and so she had a breakdown hitting her with the sandbag. The fact that Miss Bulstrode chose Vansittart over Miss Chadwick was partly because Honoria had founded Meadowbank by ‘risking it’, and Miss Chadwick wouldn’t make any changes, leading to the school’s failure.
She was played by Susan Wooldridge in the 2008 Episode of the same name. The only change from the book is that Vansittart is deleted and she hits Miss Rich instead who survives her beating. In addition, she is given the name Lettice.