Coming-of-age pictures aren’t exactly thin on the ground, and most of them are instantly forgettable. Richard E. Grant’s “Wah-Wah” is the exception. Based on his own life, it’s an incisively observed, richly detailed and wonderfully unpredictable portrait of a young man’s journey to maturity and the difficult but complicated people who accompanied him along the way.

Grant’s surrogate is Ralph Compton, whom we first meet at age eleven played by young Zachary Fox–a boy growing up in the British African colony of Swaziland; his father Harry (Gabriel Byrne) is a colonial education official (and alcoholic), and his mother Lauren (Miranda Richardson) a bitterly unhappy wife the youngster observes enjoying a session with another man, whom she ultimately runs off with. After Lauren leaves, Ralph goes off to boarding school and returns some years later now played as a fourteen-year old by Nicholas Hoult. He finds that his father has remarried, to an unbuttoned American stewardess named Ruby (Emily Watson), and Ralph, still emotionally tied to his absent mother, is initially hostile to her. Eventually he’s taken by her free-spirited manner and impatience with the humbug of the insular British community, but even she is ultimately driven away by Harry’s alcoholic rages, which threaten everyone around him. Her departure is soon followed by Lauren’s uncomfortable return. And did I mention that Swaziland is about to become independent, and that as a celebration the Brits are planning an amateur performance of “Camelot,” in which Ralph becomes involved and which the visiting Princess Margaret is expected to attend? Or that a late-coming tragedy will strike?

“Wah-Wah” is rather crowded with incident and characters–among those not yet mentioned are the abandoned wife of the man Lauren ran away with (played by Julie Walters), the haughty wife of the British governor-general (Celia Imrie), and the snooty Brit (Julian Wadham) who plans the “Camelot” event and who warns Harry about the social consequences of Ruby’s rambunctious behavior. And, true to tell, there may be a trifle too much for comfort (and the lesser British characters can come across as rather stereotypical). But the film rises above the difficulties for several important reasons. One is the quality of Grant’s script which, perhaps because it’s so closely modeled on real-life experience, avoids the superficiality of so many domestic dramas, wherever and whenever they’re set. The lead characters here come across as complex and rounded individuals, mixtures of the good, the bad and the indifferent, who frequently act in surprising, even shocking, ways. Their flesh-and-blood unpredictability is refreshing at a time when most figures you encounter on the screen are cardboard.

Of course, that wouldn’t mean much if Grant hadn’t also chosen his cast so carefully. Byrne is a revelation as the alternately genial and terrifying Harry, creating a figure at once frightening and sympathetic, and Richardson makes Lauren an icily tormented woman. Watson produces a thoroughly convincing American accent as the unrestrained Ruby, and it’s good to see Walters turn the character of the overly solicitous Gwen from a figure of ridicule to a genuinely pathetic woman. Hoult holds everything together as young Ralph; as the eye of the emotional hurricane circling around him, he has to be quietly compelling; and he is.

The performers’ success is also due to Grant’s sensitive, intelligent direction, which brings out the best in his script and steers a course between undue flamboyance and deadening understatement. The Swaziland locations are intriguing, too, and are beautifully captured by cinematographer Pierre Aim.

The title “Wah-Wah” might not be the most seductive in the world, but it has the virtue of being distinctive. And it should help you remember that this is a singularly affecting movie.