The small foyer that led to the dojo was sparse and clean. There was a check-in counter on one side, a water fountain and a couple of benches on the other. The walls were lined with posters of Bruce Lee and Jet Li, and the lighting was dim in a way that reminded me of a subterranean cave. I winked away the sunspots burned into my retinas, slipped off my shoes, and rummaged through my gym bag for my belt.

“You’re late,” Sensei said as I yanked the thick, curling strip of fabric free and shoved my bag and shoes against the wall. The belt was brown, just a few stripes away from black, but I didn’t deserve it. On my last case I’d been assaulted and had failed to employ even the most basic self-defense techniques. I was out of practice; until recently, I hadn’t attended a karate class in more than a year. My new sensei was a burly guy called Sam, and he wasn’t going to let me forget the lapse. “Twenty-twenty-twenty,” he said before I could finish peeling off my socks. “And ten extra push-ups for being tardy.”

I dropped to one knee and wrapped the belt around my waist, cinching it tight over my belly button. “Sorry,” I said. “Work stuff.”

Sensei Sam raised an eyebrow. “You’re back at work?”

“Not yet. Soon.”

He stepped aside so I could bow and enter the dojo. Then he closed the door behind me and watched as I paid my penance: jumping jacks, crunches, and push-ups. The extra ten I did twice as fast, and by the time I was finished my arms were buzzing. When I paused to wipe my brow, Sam shook his head.

“Roundhouse kicks, side kicks, back kicks, four times each way. Two-knuckle punches from horse stance until I say stop.”

I wound up into a kick and made my way across the mirrored room. I’d gotten used to Sam’s brusque style, had even grown to like it. Sam didn’t coddle me. Back in Manhattan, my karate classes had been social affairs, a dozen adults of varying ranks practicing their pinans and katas, blocks and counterstrikes. My time was spent memorizing combinations, but there was just as much palling around. Sometimes we’d go for drinks afterward at the bar around the corner. The private class I was taking in Watertown couldn’t have been more different. Here, I was entirely focused on advancement. Readying myself for what was to come.

“Faster,” said Sam, as I faced the mirrored wall and punched the air with quick, sharp thrusts. Against the peachy skin of his neck and forearms, Sam’s gi was extraordinarily black. I’d asked him once how he came to be a Shaolin Kempo master rather than, say, a professional caber-tosser. He told me he used to watch karate movies with his father before the man died of cancer. His rank, the culmination of a decade and a half of hard work, was a tribute to his dad. I hadn’t pried into his personal life since.