on the qui vive

“Like hungry little foxes,” her co-conspirators are “always on the qui vive, looking to squeeze out every bit of fun they could in the thicket of rules and regulations.”

She looked quite stunning as she walked across the dining room to the table, not at all unlike a girl on the qui vive appropriate to a big college weekend.

Madeline Grover's breathless story had set every one on the qui vive, and for several minutes everyone was wondering what all the rest would do.

What she might say next was never certain, and the uncertainty kept him always on the qui vive.

"You see, they would instantly detect any movement of ours down the hill; and by the time we got to the camp the enemy would be on the qui vive."