I had fallen into my serene state one evening, when we heard a letter dropped through the slit in the said door, and fall on the ground.
Deeming that a serene and unconscious contemplation of him would best beseem me, and would be most likely to quell his evil mind, I advanced with that expression of countenance, and was rather congratulating myself on my success, when suddenly the knees of Trabb’s boy smote together, his hair uprose, his cap fell off, he trembled violently in every limb, staggered out into the road, and crying to the populace, "Hold me!
There are no more uses of "serene" in the book.
Show samples from other sources
While I lie awake worrying, she sleeps serenely.
She remained serene even when he was yelling at her.