This is a pretty popular book. Here's a description:
A long-lost book reappears, mysteriously connecting an old man searching for his son and a girl seeking a cure for her widowed mother's loneliness.
Leo Gursky taps his radiator each evening to let his upstairs neighbor know he’s still alive. But it wasn’t always like this: in the Polish village of his youth, he fell in love and wrote a book…Sixty years later and half a world away, fourteen-year-old Alma, who was named after a character in that book, undertakes an adventure to find her namesake and save her family. With virtuosic skill and soaring imaginative power, Nicole Krauss gradually draws these stories together toward a climax of "extraordinary depth and beauty" (Newsday).