Your steps on the stairs

A man travels to Lisbon ahead of his wife to prepare their newly purchased home, while she stays in New York to oversee a research project on the neuroscience of memory and fear. Leaving behind a phase of their relationship indelibly marked by 9/11, he revels in the Portuguese capital's temperate weather and the neighborhood's calm, meticulously planning the details of their future. Yet beneath the peace and quiet of this routine, he feels a growing unease he can't explain. Is it the similarity between the two cities, and the two apartments?