A tailor in Gloucester sends his cat Simpkin to buy food and a twist of cherry-coloured silk to complete a waistcoat commissioned by the mayor for his wedding on Christmas morning. Whilst Simpkin is gone, the tailor finds mice the cat has imprisoned under teacups. The mice are released and scamper away. When Simpkin returns and finds his mice gone, he hides the twist in anger. The tailor falls ill and is unable to complete the waistcoat, but, upon returning to his shop, he is surprised to find the waistcoat finished. The work has been done by the grateful mice. However, one buttonhole remains unfinished because there was ”no more twist!” Simpkin gives the tailor the twist to complete the work and the success of the waistcoat makes the tailor's fortune. Potter declared that of all her books this was her personal favourite.