She studied the file again, focusing on a specific page. She scratched her forehead before looking at Mike. “I can’t say the patient didn’t have a window to-to move around. Nurses took his vital signs at the beginning and end of each shift. No other medical procedures were noted.”

Mike seemed satisfied with the doctor’s answer.

I picked up the file to look at the dates for myself. “What were you saying about DNA tests? How do they figure in this? Trish and Duke-is their DNA the same now?”

“Let me explain it, Alex. Bone marrow is what produces blood. It’s the patient’s blood that is diseased in Mr. Quillian’s kind of diagnosis, and this treatment aims to replace that blood production source entirely, with a healthy one.”

“So Trish’s bone marrow was transfused to Duke?”

“Right. On Day Thirty, Duke’s blood was checked. That’s done by DNA probes.” Anna turned the file around. “The old method at that time. RFLP, four probes.”

Restriction fragment length polymorphism, the original technique used in DNA analysis, had been replaced within the last ten years by PCR, polymerase chain reaction.

“What did that test tell them?” I asked.

“Whether the transplant had been a success. Thirty days out from the procedure, the DNA results on Duke Quillian revealed that all of his blood was produced by his sister’s bone marrow. That was great news, for him and his physicians. If he’d been relapsing, there would have been a mix of the donor’s DNA-Trish’s-with the blood still being produced by the host.”

“And for how long do they check it?”

“Six months. One year later. Maybe two or three in all. Someone young and otherwise healthy, like this Duke Quillian character was-well, we’d consider him cured after that. What his medical team would be hoping is that he’d die of old age, with his sister’s DNA, his sister’s blood,” Anna said.

“Not quite the ending he met with,” Mike said.

“So it’s like identical twins,” I said. “From the day of the transfusion on, Trish and Duke Quillian had exactly the same DNA.”

“With one twist,” Anna Borowski said. “It’s only in the blood samples of each of them that their DNA is alike.”

“What do you mean?”

“Duke’s hair, his skin cells, his saliva-even his sperm-all those tissues retain their original properties. Test any of them and they’re still unique to Duke Quillian.”

I was thinking of the skin cells from his fingers that didn’t match any of the blood extracted from the tunnel debris. Now the discrepancy was beginning to make sense.

“But his blood?” I asked.

“He had a perfect recovery from the leukemia, thanks to the bone marrow transplant from his sister.”

“And that means from that moment in time on,” I said, “that both of them-Duke and Trish Quillian-had blood with an identical DNA profile.”

“Just tell the lieutenant we’re in the Bronx,” I said to the detective who answered in the squad room. “We’re picking up Trish Quillian. Mike wants to go at her again, so we’ll bring her down this afternoon, if she’ll come with us.” I hung up the phone.

“I bet she has no idea what the connection was between her brother’s blood and her own DNA,” Mike said.

“You’re right. She was sixteen when they did the transplant. Not many people understood what DNA was back then. I would have thought that once the disease was cured, the patient eventually started producing his own blood again. Especially since all the rest of his DNA was intact.”

“Forget the science lesson. She’s got to know something more about Duke than she told us. And maybe it’s time for her to find out about Bex-and the pregnancy. More bones in her backyard than she ever meant to dig up. I’ve never been so happy to be spit at in my life.”

The quiet street had a series of attached houses. Once tree-lined, now there were twisted stumps and vestiges of dead trunks. Deep potholes rutted the roadway, and the cement in the sidewalks was cracked in many places.

“That’s the house,” I said, pointing ahead on the left at a small stucco building with brown shutters in sore need of a paint job.

“And there’s the detail,” Mike said, pulling over and parking in front of a gray Honda in which two detectives were sitting, in the event Brendan Quillian paid a visit.

I started to open my door to get out.

“Hold it, Coop. Slide down, keep your head out of sight if you can.”

I knew better than to ask what Mike had seen as he pulled down the visor above his head and opened the newspaper that was next to him on the front seat to screen his face.

“All clear. He’s crossing the street and getting into his car.”

When I heard the door slam and the engine start, I lifted my head. Trish Quillian was standing in the doorway, turning to take the mail from the box affixed to the side of the house.

“Who’d I miss?” I asked.

“Teddy O’Malley. I wouldn’t think by the way he runs me around those tunnels all night he’d have the strength to make a condolence call.”

“You got that dark green SUV?” Mike said to the detective in the driver’s seat.

“Ford Explorer. I wrote down the plate soon as he headed up the stoop.”

“Follow him.”

“I got orders to sit on the house.”

Mike passed his card to the driver and smacked the hood of the car. “And I’m giving you orders to get off your ass and follow him. I’ll take over the sister. Tail him, wherever he goes, and call me every fifteen minutes. Chapman. Homicide.”

The two cops looked at each other and drove off after O’Malley’s SUV.

“They got as much chance seeing Brendan Quillian coming to call as they do of ever seeing Jimmy Hoffa’s body again,” Mike said, flipping open his phone and asking to speak to Lieutenant Peterson.

We walked up the steps of the house and I knocked on the door while Mike made his call.

“Loo? Better find out who’s got the team sitting on the Quillian crib. I just sent them off on a chase, so I guess you’ll need to replace them,” he said, pausing to listen to a question from his boss. “O’Malley. My pal Teddy O’Malley. Can’t imagine why he’d be dropping in on Trish-especially without letting me in on it-but I told the two flatfoots to tell me what he’s up to.”

Trish Quillian answered the door in the same black polyester track suit she had worn to the station house, with an apron around her waist.

“Is this a bad time?” I asked.

“There’s no good one for seeing you two,” she said, untying the apron and balling it up.

“I’m sorry. Were you helping your mother with something to eat?”

“What do you care? She’s asleep. Let her be.”

“May we come in?”

Trish held the door tightly in place for a moment. Then she stepped back, leading us into the small parlor of the still house. She sat on an ottoman and Mike steered me to the sofa opposite it. The room looked as if it had been frozen in time, like photographs I’d seen of the 1950s-cabbage roses had faded on the fabric of the furniture, worn antimacassars covered the arms of most of the mismatched chairs, photographs of family members and a large framed picture of Pope Pius XII hung on the striped wallpaper, which was rolling up at the seams.

“You didn’t finish asking me what you need? You gonna keep interrupting my business every single day?” she said, looking back and forth between us, seeming more fearful than she had before.

“Your mother get many visitors, Trish?”

“You got more sense than that, Detective. Nobody much knows she’s alive.”

“And you?”

“A regular social club. Don’t it look it?”

I took in the family snapshots that represented happier days. Trish Quillian in her Communion dress; Mrs. Quillian with her young brood at the beach in Queens, where Brendan’s accident had occurred; Brendan and Duke-I guessed-as teenagers, posing with their father at an assortment of construction sites-subway and tunnel entrances, work yards filled with heavy equipment that towered over the kids, familiar landmarks such as the Brooklyn Bridge, City Hall, and the Empire State Building.