Occupying what had been the west half of banker Robert Mills's homestead is the house he is supposed to have built for his niece Minnie Knox after her marriage to John Henry Hutchings, who was a partner of George Ball and John Sealy in Ball, Hutchings and Company. Following the sale of the GC&SF Railway, in which he was an investor, Hutchings and his wife retained Clayton to transform their two-story, square-plan, Italianate house into a fantastic, stucco-faced, three-story castle, a transformation that came to seem all the more extraordinary as the spreading live oaks, palm trees, and oleanders in the house's block square park grew to maturity. The front of the house faces 29th Street and is marked by a columned porte-cochere that protrudes through a shallow, two-story-high portico, framed above the third story by paneled parapets, twin stacks, and a shallow central pediment. The south side of the house, facing Avenue O, contains a spacious one-story piazza that projects into the garden in two concave Baroque stages. The architecture of this house is without precedent in Clayton's body of work, possessing a degree of abstraction that seems to have been occasioned by the contingencies of addition and alteration.