shambles

パトロールカーを飛ばして自宅に戻った東京アメリカンクラブのプレジデント、J.B.が部屋に入ります。
J.B. pushed his way into the room. The place was a shambles. Bedding was strewn about the floor, lamps and tables were knocked over, and the pictures--some of individual family members and otheres of close friends--lay trampled and broken.
部屋の中はメチャメチャの様子ですが、不定冠詞の "a" が付いているのに複数形の様な "shambles" とは何でしょう？　辞書を見ます。
・American Heritage Dictionary:
a. A scene or condition of complete disorder or ruin: "The economy was in a shambles.".
b. Great clutter or jumble; a total mess: made dinner and left the kitchen a shambles.
・Vocabulary.com: Originally a word for a slaughterhouse, shambles now usually means "one heck of a mess," as in "You were supposed to clean your room, but it's still a shambles!
・Merriam-Webster's Online Dictionary: (noun plural but singular or plural in construction)
a: a place of mass slaughter or bloodshed: the battlefield became a shambles
b: a scene or a state of great destruction : wreckage: the city was a shambles after the bombing
c (1): a scene or a state of great disorder or confusion: an economy in shambles
(2): great confusion : mess
"s" が付く複数形で単複のどちらにもなると言う珍しい単語ですね。