Van Veen and his cousin (or sister) Ada fall in love as teenagers on an estate called Ardis, and their affair continues across decades, across a world that resembles ours but is not quite. Nabokov called it his most ambitious novel, and it may be his most difficult: dense with allusion, wordplay in three languages, and a theory of time that the narrative embodies. It is also a love story of remarkable tenderness. Nabokov published it in 1969, at seventy, and considered it his masterpiece.