the.com/thick of it

means Right in the busiest, most intense, hardest-to-escape middle of some chaotic situation or activity.

from Built from 'thick' in its old sense of 'dense, crowded part' — the thick of a forest or crowd is its most congested center, not its edges. 'Thick of the fight' or 'thick of battle' shows up in English for centuries, describing the densest, most dangerous part of combat where fighters are packed together. 'Thick of it' generalizes that battlefield image to any overwhelming situation — meetings, deadlines, drama — you're surrounded on all sides, not just grazing the perimeter.