A scene from the movie It Ends With Us. Photo: Sony Pictures/Nicole Rivelli
It Ends With Us was one of those books that suddenly seemed to sweep the world, often attracting people who don't normally read books.
It seems to be either a genre romance pretending to be something deeper, or maybe the other way round - a literary novel out to win over a bigger audience.
Lily Bloom - played by Blake Lively - seems to be the heroine of every romantic melodrama ever written.
Lily came to Boston from small-town Maine with a dream - a dream to start a flower shop.
Not just a flower shop, but the greatest flower shop ever, a flower shop for people who don't even like flower shops.
That's a big ask, obviously. But fans of romantic melodramas are pretty used to that sort of thing, and are just waiting for the arrival of those two essential characters, Mr Right and Mr Wrong.
I wonder which role Lily's best friend Alyssa's brother Ryle fills?
Yes, Ryle, the most Mills and Boone name ever, you'd think. Ryle is brooding but glamourous and, despite the designer stubble, turns out to be a successful brain surgeon. Of course he is.
As the music soundtrack - which features Britney Spears, Taylor Swift and New Zealand's own Aldous Harding - yodels away in the background, boy definitely meets girl.
But it's just a matter of time before a rival for Lily's attention comes along - someone from her past. Her first love in fact.
His name is even more soapy than Ryle, if such a thing were possible. They call him Atlas.
No wonder he looks so miserable - his school life must have been a nightmare. These days Atlas is considerably better-looking than he was on the school bus.
He seems to be a waiter these days - so no threat to a successful brain surgeon. But it turns out he owns the restaurant.
And of course, this isn't just a restaurant. It's the greatest restaurant ever, a restaurant for people who don't even like restaurants, blah blah blah.
However, his appearance sparks something in Ryle, now Lily's boyfriend. Something ugly and violent.
Just as we're wondering how Lily will choose between two equally perfect suitors, It Ends With Us plucks its rabbit out of the hat.
We're talking Fifty Shades of family violence, how even the best of prospects can have a dark side. There are hidden depths, in other words.
I admit I went into this film assuming that the 'important issues' aspect of the story would shortly be overtaken by commercial necessities.
Mr Wrong, once revealed, would be sent on his way, while Mr Right's modest charms would win over our heroine - the end.
That It Ends With Us doesn't quite continue along such predictable lines is down to one person - and no, it isn't director, producer and fictional brain surgeon Justin Baldoni.
Once again, star Blake Lively gives what could be a routine pot-boiler some unexpected class.
Lively's skill in treating a script seriously was the saving grace of films as diverse as The Shallows, The Age of Adeline and A Simple Favour.
It's entirely down to her performance that we believe in the potentially generic Lily, juggling her beautiful, if flawed, suitors.
But Lively's sincerity and likability win the day. We're even prepared to accept the happy-ending punchline of It Ends With Us.
Or is it? If you think a massive hit movie actually ends with anything, you don't know the tenacity of American capitalism.
Expect more and weaker sequels, I'm guessing, though if I were Blake Lively I'd get out while the going was good.
