Fair-Play, short for Fair-Play-is-a-Fool's-Game, is the surname of a pair of identical twin sisters who take dueling and dancing classes from Hitchcock and play a major role in The Valentine Affair.
- Carolyn Fair-Play, pronounced with a short 'i', is the 'evil twin', a thief who killed two members of the Yellow House and stole the Book of Life.
- Caroline Fair-Play, pronounced with a long 'i', is the 'good twin' and joined up with The Six.