Keystone was a bay mare bred in England by her owner Frederick Stanley, 16th Earl of Derby.

[3] Her dam Lock and Key was a minor winner and a descendant of the influential British broodmare Splitvote.

[4] Keystone was troubled with a respiratory infection in 1905[5] and made her only appearance in the Champagne Stakes at Doncaster Racecourse in September.

Despite her lack of experience she was made the 5/2 favourite ahead of the Duke of Portland's Quair (3/1) and William Bass's Gold Riach (5/1).

[11] In October she returned to form to take the £5,000 Sandown Park Great Foal Stakes, starting at odds of 1/4 and winning easily from Wombwell and Prince William.