This is a very intense, very dark read. Readers with any sort of difficulty with holocaust settings should stay away from this one.
Erich is a young German boy (15 yrs old) arrested for being gay and sent to a concentration camp. He is immediately claimed by one of the camp doctors and becomes the doctor's personal medical experiment, assistant and sex slave. He's treated to a horrific regimen of torture interspersed by affection. The torture is initially described with brutal detail; later in the story, only extraordinary punishments are described, and I maybe subconsciously thought that things had gotten better for Erich. This is of course not true - the routine torture simply became normal to Erich and not worth much thought. It's only toward the very end of the story, when Erich has flashbacks of some gruesome episodes that weren't previously described at all, that you realize how constant his suffering was the whole time.
The development of the relationship had a sort of morbid fascination for me - I think the author showed a lot of psychological acuity, and the reactions of both felt authentic to me. Certainly no artificial sweetener was added.
The language has hints of a foreign tone, and there's an overuse of commas which makes me think English may be a second language. However, there are bits of stylistic grace that are wonderful. The first time Erich catches Kaltherzig's attention: "There was something like a smile or a threat and then the eyes left him like a knife reversing out of a wound."
I found this bittersweet, not very comfortable, but compelling.