What does the cryptic crossword clue "Clothes for undercover agent whir strangely? (9)" mean?

The definition is "strangely?". The wordplay uses an anagram. anagram of AGENT + WHIR = NIGHTWEAR; definition: "strangely?" The answer is NIGHTWEAR.

Clothes for undercover agent whir strangely? (9)

Times Cryptic #28989 | 10 Across | 2024-08-07 flower