Hi, can you help me with a line i'm reading from a book please.

โกรเวอร์จ้องหน้าผมเขม็งและพูดว่า

The word i'm not sure about is เขม็ง. On looking it up i get gaze, stare or tightly twisted. It seems to being used as an adverb for จ้อง which already means to stare. So what about...

Grover stared at my face intently and said

Any help please

DS has the two together as a compound word:

จ้องเขม็ง - to fix with one's eyes, to study, to glare at

So I'd say your interpretation looks pretty good. Perhaps a less literal translation might be:

"Grover looked me straight in the eye and said..."

จ้องเขม็ง คือการมองแบบไม่กระพริบตา

no blinking while staring at someone

Thanks Softwater and Rakloke.