Rebecca seems to read the worry etched across my face before I say a word. She tells me gently that I ought to go back to my family. I hate the idea of leaving her like this, worried and uncertain, so I ask whether she’d be angry if I went home right now.

Rebecca shakes her head and admits that if she were in my place, she’d want to go home right away, too. She offers to carry the note to the factory herself while I head back to the apartment to gather my things, certain her parents will understand once I explain. Neither of us needs to say how much we’ll miss each other. As I turn and start walking away, Rebecca glances back for one last look, and we trade a small, sad wave before I round the corner.

Back at the apartment, Mrs. Rubin’s face tightens with concern the moment she hears where I’ve been. She admits she never would have sent us over to Sergei’s if she’d known we might be exposed to whooping cough. There’s a bitter irony in it, she points out. I traveled all this way trying to escape the disease, only to find it waiting in her own neighborhood. Still, she rests a hand on my shoulder and reassures me that since my visit to Sergei’s was so brief, I should come through just fine. She urges me to tell my family everything the moment I get home, just to be safe.

Alone in the empty hallway outside the Rubins’ apartment, I pull the nesting dolls apart and fit them back together. The hallway seems to tilt and blur around me, and before I can catch my breath, I find myself standing in the antique shop again, back where this whole adventure began.

Mom is still at the counter with the dealer. I call for Mom, a little too loudly, and wrap my arms around her waist so hard she laughs and asks what on earth has gotten into me. I tell her I heard something today about a whooping cough outbreak, and I couldn’t hold back my worry a second longer. Mom smiles and pats my back, reminding me gently that I’ve been vaccinated since I was a baby. My sister Megan chimes in from across the room, insisting that doctors are pretty important for exactly this reason.

The relief hits me like a weight lifting off my chest. I take a deep breath, grateful for a vaccine that Rebecca’s family has probably never even heard of. My mind drifts back to Sergei’s baby brother and to the Rubins, and a pang of worry settles over me on their behalf, since nothing protects them the way modern medicine protects my own family.

I turn to Megan, half-expecting her usual know-it-all smile, but what I find instead is something softer and sincere. She actually looks pleased, even hopeful, that I’m curious about something beyond dance for once. I give her a warm smile in return. My sister is pretty cool, I decide. I may never share her love of science, but I’m awfully glad people like Megan and Dad exist to worry about the things I never think to.