The Commodore by Patrick O'Brian

In the 17th novel in O'Brian's bestselling series of naval tales, Captain Jack Aubrey and Stephen Maturin, having survived a long and desperate adventure in the Great South Sea, return to England. For Jack, it's a happy homecoming. But for Stephen, it is disastrous, as he learns his little daughter is autistic, and his wife, Diana, unable to bear the situation, has disappeared.