McElroy’s debut novel, “The Atmospherians,” told the clever but slightly insiderly and overfreighted tale of a wellness cult designed to cleanse men of their toxicity. “People Collide” is a more agile, universal book, with its title alluding to the randomness of human connection. It’s a variety of rom-com, really, that somewhat lost art. “Circumstances pinball people together,” the narrator declares. “This is called fate because chance is too scary a word.” Perhaps no situation is more pinballish than that of in-laws, and McElroy’s unexpected digression into the psyche of Elizabeth’s mother, a frustrated writer herself who unknowingly condemns Eli for abandoning her daughter, is one of the novel’s great gifts. McElroy, who lives in Brooklyn, seems to aspire as much to flight as to eavesdropping. “People Collide” has some bumpy, odd spots — what body doesn’t? — but its naturalness and ease with the most fundamental questions of existence make it a big project knocking around in a small package, portending even bigger projects ahead.