In the first part of the book, Jakob Beer is a 7 year old child of a Jewish family living in Poland. His house is stormed by Nazis; he escapes the fate of his parents and his sister, Bella, by hiding behind the wallpaper in a cabinet. He hides in the forest, burying himself up to the neck in soil. After some time, he runs into an archaeologist, Athos Roussos, working on Biskupin. Athos secretly takes him to Zakynthos in Greece. Athos is also a geologist, and is fascinated with ancient wood and stones. Jakob learns Greek and English, but finds that learning new languages erases his memory of the past. After the war, Athos and Jakob move to Toronto, where after several years Jakob meets Alexandra in a music library. Alex is a fast-paced, outspokenly philosophical master of wordplay. Jakob and Alex fall in love and marry, but the relationship fails because Alex expects Jakob to change too fast and abandon his past. Jakob dwells constantly on his memories of Bella, especially her piano-playing, and they end up divorcing. Jakob meets and marries Michaela, a much younger woman but one who seems to understand him, and with Michaela's help he is able to let go of Bella. Together they move to Greece into the former home of several generations of the Roussos family.
The second part of the book is told from the perspective of Ben, a Canadian professor of Jewish descent who was born in Canada to survivors of the Holocaust. In 1954 the family home in Weston, Ontario is destroyed by Hurricane Hazel. Ben becomes an expert on the history of weather, and marries a girl named Naomi. He is a big admirer of Jakob's poetry and respects the way he deals with the Holocaust, when Ben himself has trouble coping with the horrors his parents must have endured. At the end of the novel, Ben is sent to retrieve Jakob's journals from his home in Greece, where Ben spends hours swimming in Jakob's past.

Question: Why is Jakob hiding? 
Answer: He's Jewish and Nazi's will kill him
Alternative answer: To excape Nazis