What kind of shop IS this?

Isabella walked down the row of shops in Hogsmeade, buying school supplies and clothing. "OOh, what is this?" She walked into a store named 'Dervish And Banges'. Sneakoscopes, mirrors, communacation galleons, and the like lined the walls. "What kind of shop IS this?" She wondered aloud. "OOOh!" She saw a really pretty necklace with a tag that said, "K.O. necklace- 15 galleons." She only had around 27 galleons left. "Should I buy it? I don't even know what it does!" She said to herself. She grabbed the necklace and walked up the the shopkeeper. "Excuse me, what does this do?"

Gwen smiled softly hopping off the counter. "Welcome to Dervish and Banges. I´m Gwen. Ah...The KO. My own creation. Press the Gem when facing your attacker and they will be knocked out cold long enough to get help or escape." She explained. "I always wear one." She smiled lifting her small silver chain showing the black stone.

Isabella smiled. "Oooh, that sounds SO COOL! I would love to buy it... It's sort of like Muggle pepper spray... But more effective." She laughed. "How much is it again? 15 galleons? I would like to buy it please," She said fingering the pretty silver-and-black necklace.

Gwen smiled and rang up the necklace. "Yep. 15. Thanks and happy Holidays!" she said handing her a a bag.

Isabellla smiled at the nice shopkeeper, and walked excitedly out of the store. She put on the necklace right away. "This thing-a-ma-bob mught be useful..." She said to herself, smiling with a glint of mischievousness in her eyes.