Adventures By Design

adverb

1. in the act of committing a misdeed
2. while performing sexual activity

Synonyms: red-handed
Etymology:
From Mediaeval Latin: while the crime is blazing; from Latin in + flagrare (burn).

Source:

“I opened my door: to wit, Mr. Boerhaave’s ursine buttocks astraddle his Blackamoor Golidilocks in my bed in flagrante delicto!”

Mitchell, David. Cloud Atlas: a novel. New York: Random House, 2004: 7.