grab (a)hold of (someone)
1. Literally, to grab and hold onto someone with one's hands. The police officer grabbed hold of the suspect before he could run away. My sister grabbed ahold of me at our mother's funeral to keep herself from breaking down in tears.
2. To gain total control, influence, or power over someone. Once major corporations grab hold of a politician, it's easy to predict where his political interests will lie. Addiction seems to have completely grabbed ahold of John.
3. To capture someone's attention, interest, or imagination. Her latest novel grabbed hold of me and didn't let go until I'd read it cover to cover.