Aminatta Forna's latest novel, "Happiness," begins with two strangers bumping into each other while crossing London's Waterloo Bridge. He is Attila, a Ghanaian psychiatrist who specializes in trauma among survivors of conflict. She is Jean, an American wildlife biologist who is studying the behavior of urban foxes in her adopted hometown.

After colliding, they go their separate ways, he still feeling "the imprint of her body on his." When their paths cross again, their lives intertwine, and for a short but significant time each leaves a mark on the other.

Attila is in town for professional and personal reasons. He must give a keynote speech at a conference but also help Ama, the daughter of friends, who has fallen afoul of immigration authorities.

When Ama's 10-year-old son Tano disappears, Attila turns to Jean for help. The pair assemble a ragtag search party composed of the West African hotel doormen, security guards, street sweepers and traffic wardens he has befriended, and the neighborhood trash collectors she uses as "informants," or volunteer fox-spotters.

As the search goes on, the pair forge a close friendship. Gradually, though, they find themselves weighed down by individual concerns.

Jean stumbles upon an illegal fox hunt, hears of plans for a fox cull and fights in vain to allay hysterical fears and change entrenched views about foxes being a menace to society. Meanwhile, a consulting case prompts Attila to reconsider all he has learned, and watching his first love, Rose, lose her battle against Alzheimer's plunges him into new pain.

Happiness, by Aminatta Forna

"Happiness" is, for the most part, a tightly focused two-hander. We warm to both of the main characters through their struggles and their solidarity in the present. However, Forna creates fuller portraits by intercutting her narrative with flashbacks of their pasts. Jean conducts a research project in Massachusetts, this time with coyotes, after which her marriage disintegrates. Attila visits the war zones of Iraq, Bosnia and Sierra Leone — "places lost in the moral darkness" — and mourns his wife. Back in London, Forna keeps us guessing as to whether Attila and Jean are capable of finding love again.

There are parts of the book in which Forna comes close to retreading old ground. Her second novel, "The Memory of Love," also followed a psychiatrist treating shellshocked survivors in civil war-hit Sierra Leone. Fortunately, Forna keeps past forays to a minimum. Instead, she develops new ways to explore common issues. Particularly impressive is her tour of hidden corners of London through the eyes of outsiders, and her examination of genuine trauma and irrational anxieties.

"Happiness" starts out as a novel about coincidence — chance encounters, twists of fate — and turns into one about coexistence: how to overcome intolerance, accept differences and live in harmony. What could have been a strident, speechifying polemic is instead a subtle, considered yet deeply resonant tale, one which sensitively and intelligently highlights connection over division and kindness over cruelty.

Malcolm Forbes has written for the Times Literary Supplement, the Economist and the Daily Beast. He lives in Edinburgh, Scotland.

Happiness
By: Aminatta Forna.
Publisher: Atlantic Monthly Press, 312 pages, $26.