I looked at her, mouth set grimly in a straight line.

His mouth set in a tight line, but he did not answer her.

Her mouth set in a stubborn line he knew so well.

Her brother's mouth set in a hard line: another expression she'd never seen on his face till now.

She seemed determined, her mouth set in a grim line.

And the mouth is more set in its ways than it used to be.

She stood up, her mouth set in a hard line.

His mouth set itself in a hard line of disappointment.

Jim nodded once, his mouth set in a tight line.

Her mouth set in a grim line, she went to the kitchen door.