It’s an obligatory listing of a horse’s bloodlines confirming its right to race on English tracks under Jockey Club rules. Bloodlines are fully documented in the Stud Book, while the register is essentially a licensing listing-every horse has to be approved and entered before being allowed in any race at any track operating under the auspices of the Jockey Club. However, along with the horse’s name and general details, each register entry contains a physical description supposedly sufficient to ensure that a given horse, with given name, age, bloodlines, and racing clearance, can be distinguished from any other horse.”

Dillon snorted. “Impossible to be a hundred percent certain always, yet armed with those descriptions, the race stewards at the tracks monitor all the starters before every race, and reexamine and verify all the placegetters after the race has been run. That’s why horses have to be entered for races weeks in advance, so the stewards can be issued with copies of the descriptions each starter should match.”

“And those descriptions come from the Breeding Register held here in Newmarket?”

“Making the stewards’ copies is what my register clerks do, at least during the racing seasons.”

“So why would our would-be thief be interested in the descriptions contained in this register? How would it benefit him?”

“I can think of two ways.” Dillon looked ahead; they were nearly at the Jockey Club’s door. “First, if his master was planning to substitute for a champion he owned, he’d need to be sure what points feature most highly in the register description, because the substitute horse would absolutely have to possess those points to make the substitution work.”

Halting before the pair of shallow stone steps leading up to the club’s double doors, he faced Barnaby. “The second possibility is that whoever has sent our thief is planning a new substitution, but hasn’t yet located a suitable substitute horse. Scanning the descriptions in the register would take time, but would unquestionably identify the best possible match for a substitution.”