Let me guess, is the blonde man named "Smith"? xD

I love the beginning! You manage to create an immersive atmosphere. The English is fluent and the wording effective, you get straight to the point. The introduction is great.

However, the torture session seems a bit extreme, and too rushed. Everything is over in less than a week, they already destroyed his family, I don't think it's the way real torturer would act. Instead, they would let him think they might torture his family, without giving him actual proof. This way, he will be forced to imagine how they torture his family (I'm repeating myself too much...), which is worse than just seeing them torture it.  Torturer take time to exhaust their victim, wake him up in the middle of the night, bring him to the limit of his resistance, both physically and psychologically (Did you read "Schachnovelle", von Stefan Zweig? Their method is really wicked). This can't be reached in one day, and doesn't justify a change in Smith's method. He looks like an amateur here.

The ending is really rushed, it's the usual scheme "TF + escape and then all is well". I expected you to develop what happened after! Even a dragon couldn't escape so easily, except if the tormentors wanted him to. It doesn't explain why the serum (which has been extensively tested) has a fully different and much more complicated effect than the one he tested on rats (except if it's not the same serum). Plus, I believe no sensible tormentor would TF him into a killer beast. They would rather incapacitate him progressively, make him lose control over parts of his body, making him unrecognisable, everything they need to deprive their victim of hope.

It is rather hard to manage an interesting torture scene. Maybe you read "The Farseer Trilogy" (Robin Hobb), in which the main character gets tortured once. It lasts much longer than here and has psychological and physical consequences all over the story. He only escapes by luck, and his attempt almost fails. What is interesting is the consequences : he needs help from the outside, because his tormentors do everything they need to make him unable to defend himself. It brings a lot to the story, and isn't lightly dealt with. You can't just say "ten years later...", we expect to see how deep he was hurt and how he will heal from this experience, or it will seem gratuitous.

To conclude, I think this chapter has a really good intro, but you could improve its ending, by developing the personality of the people or by skipping most of the torture. For example, you could make your character tell his memory of how he got TFed. This way, you could develop his personality by chosing what you want him to tell, create an atmosphere with these choices, and skip all the difficult explanations without making it clumsy (his memory isn't perfect, or he didn't want to tell...)

Smaller remarks:
"so the room must be dark as well" : you said his vision was blurry, so there must be light. But here it seems it's dark. This part confused me a little.
"what I already had feared two men were" : there's punctuation missing.
"I don’t now" : "know"