An early collection of short stories, all but one told in the first person, many of them teenagers or young men, yet their voices invariably ring true. Some events are shocking and depraved, but even in those stories, you get an uncomfortable but plausible and powerful insight into the mind of the perpetrator.
Although you could easily read the book in one sitting, it’s probably best to read one story at a time, interspersed with other things, as many will leave a nasty taste in your metaphorical mouth.
NB McEwan was only 27 when this was published, and three years later, there was the equally shocking "Cement Garden" (https://www.goodreads.com/review/show/280183770). He still writes about appalling acts, but he's matured and developed some subtlety.