We know from the second sentence of Last Night in Montreal that protagonist Lilia disappears, but it is the first sentence — “No one stays forever” — that defines this beautiful, complicated, and occasionally disappointing debut novel. Lilia enters grad student Eli’s spartan and stable life one day at a coffee shop. She has a bohemian beauty (Eli finds her choppy, self-barbered hair “thrilling”) and a fascination with his study of dead and dying languages. At first, this seems to hold the key to Mandel’s plot: We constantly misinterpret the words of the people we love. It’s less important to know about Eli than to know he cares enough about Lilia to try and understand why she, in her own words, “doesn’t know how to stay.” Lilia, used to an itinerant lifestyle after years of moving rapidly with her father, leaves Eli in one city and pops up in another, living with the mysterious Michaela. Michaela’s father, police officer Charles Graydon, is also chasing Lilia — but his reasons for doing so couldn’t be more different from Eli’s. Unfortunately for plot cohesion, at this point the idea that “no one stays forever” takes over, and sometimes remembering why an event or character matters takes effort. Fortunately for Mandel’s future as a novelist, that theme was the right one to pursue. The author is concerned with the different faces of neglect and their consequences. Once Lilia’s full story is revealed, characters understand each other all too well — and perhaps too late. Mandel’s exquisite use of language and pacing mean that every last word counts, up to the very last sentence.