It It starts like this. I am picking up my daughter from day camp on the shores of Lake Michigan and taking her to Wrigley Field. Zoë likes the Cubs, so I thought I would surprise her with a game. It''s a pretty day, and as we bike along the brownstone streets of Chicago''s Lakeview neighborhood, my daughter on the bike seat behind me with her curly hair blowing in the wind, we are the vision of summer. We enter the crowd and I buy two tickets behind home plate. Zoë is almost five, small for her age, so she sits on my lap so she can see better. As the game starts, I throw my left arm around her body, my hand cupping her side, and there, under her ribs, I feel a bump. I don''t make much of it, though at night I mention it to Elise.

It feels like an extra rib, though there isn''t one on her right side. Neither of us is concerned; never­theless, in the morning I make an appointment with our pediatrician, just to be safe. The next day I take Zoë to the pediatrician, who feels Zoë''s side and says the bump is probably a cyst, and will go away, though the following day it feels bigger. On Saturday we go to another game at Wrigley Field, this time with Elise and Zoë''s little sister, Mia. The Cubs lose, as they do, but everyone has a good time and we take a family photo next to the field after the game. As a precaution we had scheduled an ultrasound, so on Mon­day morning Elise brings Zoë and Mia to a nearby imag­ing clinic. Elise is finishing her postdoc in Chicago and will start teaching at NYU in the fall. We are moving to New York in two weeks.

I write children''s books and have to sketch an illus­tration this morning for my next book. My desk in our second-floor apartment looks over a quiet street of brownstones and shaded trees, and I am standing next to my desk, sharpening my pencil and staring out the win­dow when the phone rings. It''s Elise, and her voice is quiet, and she is saying there is a tumor on Zoë''s kidney and I am watching the leaves outside the window turn in the morning light, waving and bobbing in the breeze--tumor, kidney, kidney, tumor--and I listen to Elise, and I don''t think the word "cancer" is said by either of us, and it''s such a pretty day, and then I am out the door. We meet at the edge of our local park, Elise coming toward me with the girls in their jogger. We hold each other, and I give each of my daughters a kiss on her head--they are happily playing with each other--and Elise and I hold each other again. The next days are blurry, but everything we do is very precise. We call our pediatrician. We arrange to meet the oncologist.

We go to Children''s Memorial Hospital across the park and meet the oncologist, a smiling man with small glasses. He tells us Zoë has a pediatric kidney cancer called Wilms'' tumor, a "good cancer," a funny pair­ing of words. Surgery is scheduled, as soon as possible, two days from now. We meet the surgeon, who shows us on a monitor the tumor surrounding Zoë''s kidney. It''s a dark mass, unreadable. We make more phone calls. Par­ents, insurers. When one of us is on the phone, the other is with the girls.

Our minds are never where we are. Elise calls NYU and tells them we have to delay our move to New York. I call the publicist for a book I wrote about being a father--the paperback is coming out next month--and tell her I won''t be able to do all the things I said I was going to do. I hear in her silences she doesn''t know what to say. I call friends back east. I reach one as he''s driving to the city from Fire Island and in the back­ground I hear seagulls. We go to a beach on the lake with Zoë and some of her friends. As the girls play in the water, we talk with the parents, keeping our voices level with nothing-to-see-here expressions on our faces.

At night we tell Zoë the growth on her kidney needs to come out, and how that will happen, and that everything will be okay. Zoë looks at us and nods. We tell Mia that her sister needs to go to the doctor and that everything will be okay. Mia nods too, like her sister. We take baths. On Zoë''s left side we are able to see the tumor now. In two days it has grown and is rearing out from under her ribs, like something inside punching outward. We sit on the couch and tell bedtime stories.

Once the girls are asleep we call friends who are doc­tors, and at midnight we read and reread the Mayo Clinic website, our apartment illuminated by the soft glow of computer screens. Numbers and percentages, probabilities of survival. Numbers that, once learned, we will never not know. We are experts now. We know the numbers. Then we shut down our computers and lie in bed. Zoë''s day camp is in a church across the street from Children''s Memorial. On Thursday we pick Zoë up.

She''s wearing her nursery school T-shirt. The drawing of the child on the shirt looks like Zoë, with its curly hair and small smile. She looks no different than she did last week. We bring her stuffed tiger, and we walk across the street. Hours of drinking fluids and fasting, reading books in the bright light of the waiting room. Plastic chairs circle the room, and down one corridor comes a distal hum. Empty halls seem to lead everywhere. Then it is time, and as Zoë is led away by a nurse through a swinging door we tell her we will see her very soon.

We wait. An hour, five hours. The surgery takes longer than it is supposed to--a soundless television with breaking news hangs from the ceiling above us--then we are summoned and meet the surgeon in a windowless room. The surgeon looks tired. There were complica­tions, the tumor broke apart. The surgeon removed the tumor, and the kidney, and had to remove part of the colon, too. The cancer is stage three, which is not good. But I am not thinking about that and we are led to Zoë, and we are able to see her, and she''s asleep.

So peaceful and so pretty, her head resting on her stuffed tiger, tubes spiraling out of her. I don''t remember when she woke, I don''t remem­ber when I went to bed. In the next days Elise and I are always with her, or shuttling home to be with Mia. We take turns, though at night it is mostly Elise. We set up camp in Zoë''s room in the hospital. During the day we go to the playroom, Zoë rolling on the stand that holds her IV and wearing a green gown that covers the horizontal stitches on her side. We bring Mia to visit. She clambers onto her sister''s bed.

They share pancakes. The days are hot, the evenings cool, and at midnight I bike through empty streets to the hospital, though it is only two blocks away. I try to sleep on the chair at Zoë''s side. At four in the morning we are woken by a pack of white-coated residents who watch us from behind clip­boards. After six days, Zoë comes home. The next week we bike downtown to Northwest­ern Memorial Hospital for radiation. The radiologist is round and South Asian and friendly. His four assistants draw on Zoë''s belly, measuring to the millimeter, in blue ink.

Then she is slid flat into the radiation machine. Zoë''s stuffed tiger goes in the machine, too. "It''s all in the biology," says the radiologist as we wait in a control room bleeping with screens, giving me a big grin. Everyone here is so cheerful. On the bike ride home Zoë throws up. We don''t hear her at first. She''s tough, the kind of child who doesn''t want people to see her cry. In the next weeks she has nine more radiation treatments, and she starts chemotherapy.

We have more appointments at Children''s Memorial. We call doctors at Memorial Sloan Kettering in New York. We call doctors at NewYork-Presbyterian. We meet our oncologist. He tells us Zoë''s histology is good, though I''m not exactly sure what that means. We plan our daughter''s treatment and the continuing chemotherapy she will receive in the fall. "It''s going to be okay," the oncologist says before we leave the last time, giving me a hearty handshake. Is it? What is "it"? This unspoken it.

But we know what it is. It is everything, and it is all in the biology, and it is what we have become, and we would think more about it but we have a birthday party to plan. We had to cancel Zoë''s birthday party when she was in the hospital, so now we plan a shared birthday party for her and Mia. Elise bakes a cake with butterflies and bugs in the frosting and our friends gather in the local park. The day is humid and we lead the girls and their friends on a scavenger hunt through Oz Park, following clues we taped to the statue of the Cowardly Lion and the Scarecrow. Then we eat pizza in the shade. Just another festive, manic birthday party, interrupted by a dog steal­ing the pizza. But even that doesn''t matter and the girls blow out the candles.

Zoë is five. Mia is three. We slice the cake, and afterward the children go to the playground with Elise as I clean up, and here''s that dog again, a silvery Weimaraner, and this time he''s going for the cake. What the hell? I look around for the dog''s owner and see him standing to the side in shades and a button-down shirt. "Hey, watch your fucking dog," I say. The man tells me to watch my language, tells me that children are present, tells me something about his being a lawyer, but I am reaching for a piece of cake. Throwing a piece of cake is not easy, especially one covered with frosting. As the piece of cake flies through the air--my throw underhanded and weak--I think about that second baseman who played for the New York Yankees a few years ago.