Ian McEwan, in this compact novel, has taken a microscopic look at one evening in the life of two young people, their wedding night. It's impressive how he can maintain the concentration necessary to enumerate the minute emotional details of each of his characters.
McEwan's genius is the ability to define a pivotal event, a moment in time when everything changes. If one person had said one word differently or turned to the right instead of to the left, the rest of time would be altered for everybody forever. He is able to make the reader think that his characters' fates are important, and to let us see the crisis looming ever closer and keep hoping it will turn out for the best--but in McEwan's books, it rarely does.
The suspense in On Chesil Beach is what will transpire when the two protagonists, both virgins, share the experience of their initial sexual encounter. They have very different points of view. The novel is exquisitely detailed in exploring their two viewpoints and making it clear to the reader that the two of them have no insight into each other's thoughts. Their culture discourages them from frank discussions so instead of telling each other about their hopes and fears, they just think to themselves, and the tension builds.
I won't reveal how the story unfolds, but it's not too much of a spoiler to say there's no happy ending--it is pretty obvious from the beginning that unless some miracle occurs these two hopelessly unprepared people with their ridiculous expectations and paralyzing anxieties are bound to misunderstand each other, and destined to hurt each other. A sense of humor might save them, but there is no evidence either has one.
This subject has been treated before but I've never seen it done so explicitly and with such literary skill. The main literary device is the beach as a metaphor. This particular beach where they are planning to spend their honeymoon has the peculiar quality of having pebbles of graduated size--"...thousands of years of pounding storms had sifted and graded the size of pebbles along the eighteen miles of beach, with the bigger stones at the eastern end. The legend was that local fishermen landing at night knew exactly where they were by the grade of shingle." (p.23) The newlyweds picture themselves walking along the beach, observing scientifically, testing the truth of the guidebook that tells the story of the pebbles. That could be their life together, a shared progress through the years, steadily becoming older and more comfortable, growing in wisdom and prosperity, having children, weathering the inevitable storms and becoming stronger for it. That would be the natural outcome of their wedding. Because they are not comfortable with nature, their fate is something else.