John T. Foster

American author of children's novels and also a number of factual books about various historical events. His children's series about a character called Marco, a young amateur sleuth, are probably his most well known books. He wrote one horse story (based on true events) set in the world of trotting races. I am not sure if the author had any connection to horses however.

Horse and Pony Books:

(DODD MEAD [USA] 1974)
SUMMARY: Historical horse story based on the real-life horsy heroine, Lady Suffolk, the 'Old Gray Mare' who was a record-breaking trotter in the 18th Century.
The gray mare has been abused in the past but has not lost her spirit. When she is helped by a caring young part-Indian boy, things begin to look up for her.

Collector's Info:
Easy to find in America and usually low cost. Harder to find elsewhere but buying from America should not prove too expensive, even with shipping costs.