Her foals included the top class colts Rhodes Scholar and Canon Law, the influential broodmare Highway Code and Archive, a racehorse of no account who sired Arkle.

[5] Book Law made her first impact in June 1926 when she contested the Queen Mary Stakes at Royal Ascot in which she was ridden by Robert A "Bobby" Jones and won at odds of 7/2.

[8] In a twenty-eight runner field for the 1000 Guineas over the Rowley mile at Newmarket Racecourse on 29 April, Book Law dead-heated for second place with Endowment, two lengths behind the winner Cresta Run.

[6] On 7 September, with Jellis in the saddle, Book Law started the 7/4 favourite in a field of sixteen colts and fillies for the 152nd running of the St Leger over 14+1⁄2 furlongs at Doncaster Racecourse.

[15][16] Three weeks after her Leger success, Book Law ended her second season with a run in the jockey Club Stakes over fourteen furlongs at Newmaarket in which she was matched against older horses.

[19] When Alec Taylor the Manton stable was taken over by his assistant Joseph Lawson Book Law began her second season by winning the Burwell Stakes over 1+1⁄2 miles at Newmarket in May.

She ended her career with earnings of £31,875, making her the fourth most successful female racehorse in British turf history up to that time behind Sceptre (£38,283), Pretty Polly (£36,638) and La Fleche (£34,703).