Sandy Johnson is the official farrier of the Washington International Horse Show. A former junior equestrian standout in Europe, Johnson left Ireland at age 18 to become a groom for a number of international riders across Europe before coming to the U.S. (Matt McClain/For The Washington Post)

It was early Tuesday morning when Sandy Johnson realized that the inside of a champion horse’s foot had gone missing.

Idling in her cramped workspace outside the Washington International Horse Show, where the day’s first whinnies were echoing throughout Verizon Center, the longtime farrier saw a lame brown gelding and an anxious owner approach. The horse needed a new horseshoe, its owner told Johnson. It needed it now.

Removing shoe from hoof, Johnson saw bands of daylight poking through the nail holes. Not good. They would need to build an artificial foot, Johnson told the owner. As it stood then, molding a new horseshoe would be like trying to add extensions onto fake fingernails.

“No,” Johnson recalled being told. “Just get the shoe on. We’ve got to go in the ring now.”

Johnson got the shoe on. The horse got to the ring, where it won its class. But the incident also got to the British-born Irishwoman’s very nerves. She told the owner she and her horse needed to come back tomorrow. The horseshoe was on “by a thread and a prayer,” Johnson said later, and she didn’t want a lame horse to become a lost one.

“You ever hear that one, ‘For Want of a Nail?’ her assistant, Gunner Gatski, asked a show official standing nearby as Johnson grinned. For want of a nail, the old saying goes, the shoe was lost. For want of a shoe, the horse was lost. Ultimately, the kingdom is lost altogether, and, in a way, the farrier is to blame.

The only blame that morning fell on the owner. Her perfectionist sensibilities aside, Johnson knew that much. Being the horse show’s official farrier offers a certain cachet in the equestrian world and a nice paycheck — the baseline cost for a full set of shoes is $350 — but it also brings with it an inviolable mandate: Do whatever the owner wants.

That suits Johnson just fine, because this is what she wants to do. A former junior equestrian standout in Europe, Johnson left Ireland at age 18 to become a groom for a number of international riders across Europe. Offered a job in the United States, Johnson arrived stateside to find that within three months, she’d found her future husband, Joe, a farrier himself, and her calling.

“We were traveling 300 days a year [for work],” Johnson said. “Either I went or I was alone.”

The knowledge seeped into Johnson’s subconscious, and when Joe broke his ankle six years ago, his prize horses needed a farrier. His wife did just fine.

She didn’t know then what she knows know — like how to fix what’s known as a horse’s “confirmation” so that its legs jut out less like the Leaning Tower of Pisa and stand more like the Washington Monument, or how to tell when a pony might need the equine equivalent of the Dr. Scholl’s treatment — but it never hurt business. Johnson has businesses in Ohio and Kentucky in addition to the one she shares with Joe in Florida. They don’t want for much, certainly not a nail.

Still, Johnson happily made time for Washington. On Tuesday, as she and Gatski readied for the crush of horseshoeing this weekend’s top events will entail, regarding it with an equal mix of dread and delight, Johnson reached for another old saying.

“You know the adage, ‘No foot, no horse?’ ” Johnson said. “It’s true.”