Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Morbid But Hopeful
From pretty much the beginning of the book, we know that Jacob dies during World War II—we're just not sure exactly how it happens. It's almost like we're reading the book backwards, since we already know what happens because the younger Jacob tells us he's there to visit his grandpa's grave.
However, it's not until the end that we begin to understand the meaning of all the morbid overtones. When Geertrui realizes she wants to confess her affair with Jacob to Sarah, she's got no time left herself, thanks to terminal stomach cancer and a set date for her own euthanasia. Daan and Tessel have to come to terms with the fact that Geertrui is in so much pain she'd rather die than keep on suffering, while Jacob knows the truth about his grandpa will crush his grandma, but thinks he should tell her anyway. Not exactly light stuff, is it?
Sometimes, Geertrui uses what she knows now to tell us about what was happening then. Take the moment she leaves her folks:
A terrible moment, when it was necessary for everyone's sake to appear calm and cheerful. A pretense I would not have been able to sustain had I known this would be the last time I would see my father. He died during the Winter of the Hunger that was visited upon us after the failure of the Allies to liberate my unhappy country until the spring of 1945. It is as well that the future is ever an unread book , for had I known I would never see Papa again, I could not have left him. (7.64)
In the moment, she's hopeful and praying something good will come of her running off with Dirk, Henk, and Jacob—but looking back, she knows some terrible things came out of that time too. So we get both perspectives together—the hopeful tone Geertrui possessed at the time, and the morbid one she brings to the moment in retrospect. The book is filled with moments when hope and death collide, and the tone follows along accordingly.