I heard Lydia Millet asked once, in an interview, why she’d left the literary world of New York, where she clearly thrived, and she said it was too easy to be mean there, and she’d rather be nice, or words to that effect. And niceness is not generally considered a literary virtue, but in Millet’s work generally, and her new novel “Dinosaurs” specifically, it certainly is.

Niceness, in fact, is the defining trait of the novel’s protagonist, Gil, who, after the abrupt and unhappy ending of a 15-year relationship, has purchased a house, sight unseen, on the outskirts of Phoenix, and walked there, over the course of five months, from Manhattan.

Gil, an orphan raised in an austere fashion by his grandmother, is the heir to an oil fortune, uncomfortably conscious of his privilege and committed, in a modest way, to doing good works. In his new house (“he thought of it as a castle”) he becomes involved with the family that lives next door.

As he, almost incidentally, becomes the friend, guardian and babysitter of that family’s 10-year-old boy, Tom, Gil volunteers at a shelter for abused women, hunts for whomever is shooting birds in the neighborhood, and contends with the pitiful man who’s gotten out of prison for running over Gil’s parents when Gil was a child.

This all unfolds in the most natural way, with current moments tracing back to Gil’s past, and the sense of his character accumulating from quiet moments with Tom, Tom’s parents and Sarah, a new, slowly emerging love interest. And through it all, there is a concern about what’s happening in the world, depredations environmental, political and personal.

It’s hard to say why this is so involving and moving, but it is. When someone bullies Tom, when the dead birds are discovered, when Gil’s friend in New York makes a painful sacrifice, Gil’s moral compass is dead-on, but his choices are not easy, and the results are anything but guaranteed.

In short, you like the guy, because he’s nice but also because being nice is difficult, revelatory, and, finally, satisfying.