My sister Melanie won’t let me help with the time capsule we’re making. Four years older and in junior high now, she likes to boss me around. She’s searching the attic for things to put in the box when I give up and head down the stairs. I take the last three steps in one giant jump, then wish someone had seen me.

With Melanie in the attic, the living room seems too quiet, so I check behind the sofa for outlaws. I worry about burglars and other things too: quicksand, copperheads, lockjaw, leprosy, nitroglycerin, the atom bomb, the Russians, and, most of all, fallout. You can’t see fallout or feel it coming until it has stolen through the walls of your house. I press my ear to the floor and listen for stampeding cattle, then get up and go look for my mother.

Every Fourth of July our family has a picnic down by the river at dusk. We gather driftwood for a fire, roast hot dogs until they blister and drip onto the flames, and watch shimmering fireworks shot from the yacht club across the channel. My father strums his guitar, singing “Kingston Town” and “Charlie on the MTA.” His voice is as deep as the ones on the radio and pulls us toward the sandy blanket by the fire. Our mother used to harmonize when our father sang “Moon River,” but these days she gazes at the dark water as if something she needs may be out there. When the only lights left are embers and fireflies, and our house glows white on the hill, Melanie and I shake out the blanket and try not to step on spent sparklers. There have been years when I was the only person with a band-aid when one was needed, but usually no one gets hurt if I’m prepared.

Suddenly I don’t care if Melanie makes the time capsule without me. I’ll make a first-aid kit instead. I choose my madras purse to be the kit and begin to look for things to fill it.

In the downstairs bathroom I balance on the edge of the green tub to reach the medicine cabinet and select an almost-empty tube of bacitracin. Behind the toothpaste I discover a red-brown bottle of mercurochrome, and, after opening it to admire the tiny glass wand attached to the cap, I twist it closed and drop the bottle in as well. I add tweezers — in case someone gets a splinter on the pier — gauze for scrapes, and syrup of ipecac in case someone is poisoned.

I wander into the living room, where the picture window frames my mother’s favorite view of the river like a painting. Usually the water sparkles like stars flashing on and off, but today it is flat and still. The sky is blue, but white and gray thunderheads are building over the opposite shore. I squint, imagine they are mountains, and wonder how I would save us in case of a tidal wave.

My parents’ voices are raised in their first-floor bedroom. I add a sewing needle and thread to the kit in case someone tears her shorts, then pad across the braided rug like an Indian scout. I’m on the lookout for danger and don’t make a sound, my worn flip-flops as silent as moccasins. I halt where the rug ends to scan the dining-room territory. Down the short hallway my parents’ voices grow louder. My mother says, “Please love me, David,” or maybe she says, “He loves me, David.” I don’t know. Even holding my breath, it is almost impossible to hear them clearly from behind their closed door. They stop, and I imagine my mother sitting on the quilt she sewed from Melanie’s hand-me-downs that even I’ve outgrown. My father, his back to her, looks at himself in the mirror or through the window to the road. In the silence I slip into the kitchen to get two popsicle sticks for a finger splint, baking soda for bee stings, my jump-rope in case of quicksand, and a tea towel for a tourniquet. I drop in a paring knife to treat snakebites, but I’m not sucking Melanie’s leg if it’s her. The more things I add, the better I feel.

My parents’ bedroom door opens, and my mother walks past me barefoot, as if I’m not there, the smell of Shalimar in the air as she passes. In the kitchen she returns to making brownies, yanking a spoon in circles through the thick mix like she’s furious with it. She stops to tap two brown eggs against the rim of the bowl. Dropping the yolks into the batter, she tosses the whites and shells into the sink. The egg whites look like two jellyfish.

“What are you up to?” my mother asks, but she does not look at me. I place my madras purse on the counter next to the brownie bowl, so close that they are touching, and I tell her about the first-aid kit.

“Is someone planning to get hurt?” she asks.

It’s not really a question, any more than How would you like a spanking? But I say, “You never know.”

After she spoons the thick chocolate batter into a greased pan, she shoves the brownies into the oven and shuts the door with a thump that makes the red teakettle jump on the burner above. She turns to me and cups my cheeks in her soft, cool hands.

“Stop scowling. Your face could freeze that way.”

I think I am wearing my regular face, so I hold the look and walk to the hall mirror without blinking. I move like I’m balancing a book on my head — rigid and regal — as if my expression might fall off if I stumble. I see brown eyes beneath straight brows, a sunburned nose, not as pretty as Melanie’s, with more freckles on it now than there were in June. I wouldn’t call my expression a scowl, but I do look worried. I force a big smile, which, with my frowning eyes, looks almost scary. As I’m about to turn to show my mother, there is a crash behind me and a shout. A glass milk jug lies on the floor, and my mother sits next to it grasping her ankle. The bottle isn’t broken, but milk chugs out of its mouth and spreads in a growing puddle beneath the cabinets. My mother rocks back and forth, her forehead pressed to her raised kneecap. I run to her to see if I should call my father for help, but I hear the screen door slap shut and the car engine start.

“Mommy?” I say, crouching down. “Let me see.” I tug on her hands, but she won’t do what I say. She just continues to rock, eyes closed, head down.

“Move your hands,” I command, but she continues to sway, so I soften my voice and lay my hand on her back. “You’re OK, you’re OK, you’re OK now.” I sing the words softly, just as she has sung them to me, but I don’t know how to help her or what to do. My first-aid kit has fallen from the counter to the floor. Gauze, baking soda, popsicle sticks — everything — has spilled in the widening path of the milk.

I pat her now as she sobs softly. When she finally does raise her head, I’m less sorry for her than I am afraid. I have never, in my whole life, seen my mother cry, and something inside me seems to fall away, as if the ground beneath my feet is only air. My heart pounds against the wall of my chest, and we both look down at her slim ankle as she slowly lifts her hands.

There is no cut or bruise, nothing broken that I can see. I stand up and pull back. “You’re not that hurt,” I say, as if she has tricked me or lied, but she just sits there and sobs. “That’s too many tears,” I say loudly, like she is breaking some rule. Finally I shout, “Get up!” I sound angry, but the truth is I can’t breathe.

When my mother won’t stop crying, I decide to see if Melanie has finished the time capsule and whether any of the stuff she’s put in it is mine. It has to be buried today, she says, so that the date will be easy to remember: July 4, 1964. We will open it fifty years from now to remember who we were: a family in a white house by a blue river, before fallout found us.