It was a clear, calm, lazy April morning, the day the worst week of my life began.

I was jogging down by the bay with my border collie, Martha. It’s my thing Sunday mornings—get up early and cram my meaningful other into the front seat of the Explorer. I try to huff out three miles, from Fort Mason down to the bridge and back. Just enough to convince myself I’m bordering on something called in shape at thirty-six.

That morning, my buddy Jill came along. To give her baby Lab, Otis, a run, or so she claimed. More likely, to warm herself up for a bike sprint up Mount Tamalpais or whatever Jill would do for real exercise later in the day.

It was hard to believe that it had been only five months since Jill lost her baby. Now here she was, her body toned and lean again.

“So, how did it go last night?” she asked, shuffling sideways beside me. “Word on the street is, Lindsay had a date.”

“You could call it a date … ,” I said, focusing on the heights of Fort Mason, which weren’t getting closer fast enough for me. “You could call Baghdad a vacation spot, too.”

She winced. “Sorry I brought it up.”

All run long, my head had been filled with the annoying recollection of Franklin Fratelli, “asset remarketing” mogul (which was a fancy way of saying he sent goons after the dot-com busts who could no longer make the payments on their Beemers and Franck Mullers). For two months Fratelli had stuck his face in my office every time he was in the Hall, until he wore me down enough to ask him up for a meal on Saturday night (the short ribs braised in port wine I had to pack back into the fridge after he bailed on me at the last minute).

“I got stood up,” I said, mid-stride. “Don’t ask, I won’t tell the details.”

We pulled up at the end of Marina Green, a lung-clearing bray from me while Mary Decker over there bobbed on her toes as if she could go another loop.

“I don’t know how you do it,” I said, hands on hips, trying to catch my breath.

“My grandmother,” she said, shrugging and stretching out a hamstring. “She started walking five miles a day when she was sixty. She’s ninety now. We have no idea where she is.”

We both started to laugh. It was good to see the old Jill trying to peek through. It was good to hear the laughter back in her voice.

“You up for a mochachino?” I asked. “Martha’s buying.”

“Can’t. Steve’s flying in from Chicago. He wants to bike up to see the Dean Friedlich exhibit at the Legion of Honor as soon as he can get in and change. You know what the puppy’s like when he doesn’t get his exercise.”

I frowned. “Somehow it’s hard for me to think of Steve as a puppy.”

Jill nodded and pulled off her sweatshirt, lifting her arms.

“Jill,” I gasped, “what the hell is that?”

Peeking out through the strap of her exercise bra were a couple of small, dark bruises, like finger marks.

She tossed her sweatshirt over her shoulder, seemingly caught off guard. “Mashed myself getting out of the shower,” she said. “You should get a load of how it looks.” She winked.

I nodded, but something about the bruise didn’t sit well with me. “You sure you don’t want that coffee?” I asked.

“Sorry …You know El Exigente, if I’m five minutes late, he starts to see it as a pattern.” She whistled for Otis and began to jog back to her car. She waved. “See you at work.”

“So how about you?” I knelt down to Martha. “You look like a mochachino would do the trick.” I snapped on her leash and started to trot off toward the Starbucks on Chestnut.

The Marina has always been one of my favorite neighborhoods. Curling streets of colorful, restored town houses. Families, the sound of gulls, the sea air off the bay.

I crossed Alhambra, my eye drifting to a beautiful three-story town house I always passed and admired. Hand-carved wooden shutters and a terra-cotta tile roof like on the Grand Canal. I held Martha as a car passed by.

That’s what I remembered about the moment. The neighborhood just waking up. A redheaded kid in a FUBU sweatshirt practicing tricks on his Razor. A woman in overalls hurrying around the corner, carrying a bundle of clothes.

“C’mon, Martha.” I tugged on her leash. “I can taste that mochachino.”

Then the town house with the terra-cotta roof exploded into flames. I mean, it was as if San Francisco were suddenly Beirut.

“Oh, my God!” I gasped as a flash of heat and debris nearly knocked me to the ground.

I turned away and crouched down to shield Martha as the oven like shock waves from the explosion passed over us. A few seconds later, I turned to pull myself up. Mother of God …I couldn’t believe my eyes. The town house I had just admired was now a shell. Fire ripped through the second floor.

In that instant I realized that people could still be inside.

I tied Martha to a lamppost. Flames gusted just fifty feet away. I ran across the street to the blazing home. The second floor was gone. Anyone up there didn’t have a chance.

I fumbled through my fanny pack for the cell phone. Frantically, I punched in 911. “This is Lieutenant Lindsay Boxer, San Francisco Police Department, Shield two-seven-two-one. There’s been an explosion at the corner of Alhambra and Pierce. A residence. Casualties likely. Need full medical and fire support. Get them moving!”

I cut off the dispatcher. Procedure told me to wait, but if anyone was in there, there was no time. I ripped off my sweatshirt and wrapped it loosely around my face. “Oh, Jesus Christ, Lindsay,” I said, and held my breath.

Then I pushed my way into the burning house.

“Is anyone there?” I shouted, choking immediately on the gray, raspy smoke. The intense heat bit at my eyes and face, and it hurt just to peek out from the protective cloth. A wall of burning Sheetrock and plaster hung above me.

“Police!” I shouted again. “Is anyone there?”

The smoke felt like sharp razors slicing into my lungs. It was impossible to hear above the roar of the flames. I suddenly understood how people trapped in fires on high floors would leap to their death rather than bear the intolerable heat.

I shielded my eyes, pushing my way through the billowing smoke. I hollered a last time, “Is anyone alive in here?”

I couldn’t go any farther. My eyebrows were singed. I realized I could die in there.

I turned and headed for the light and cool that I knew were behind me. Suddenly, I spotted two shapes, the bodies of a woman and a man. Clearly dead, their clothes on fire.

I stopped, feeling my stomach turn. But there was nothing I could do for them.

Then I heard a muffled noise. I didn’t know if it was real. I stopped, tried to listen above the rumble of the fire. I could hardly bear the pain of the blistering heat on my face.

There it was again. It was real, all right. Someone was crying.