Originally from this prompt.

“Alright rookie, let me fill you in.” Detective Rick Rogers gestured to the ball below, “Those murders we’ve been keeping off the news are by the same person. Some Sound of Music loving psycho is working his way through the song My Favorite Things, line by line. The first body was found in the rain covered in roses. The second was killed with by a blow to the head from a copper kettle, and the murderer left mittens on at the scene. We only figured out the pattern with the third body, which was delivered to the station in a brown paper package, tied up with string. We’ve been trying to stop the murders since, with no luck. Wild ponies, poisoned strudel, exploding bells, weaponized schnitzel and nocturnal rabid geese; we didn’t see any of it coming.” Rogers shuddered at the memories.

The rookie, Hannah Stein, was counting off the lyrics on her fingers. “So… we’re on ‘girls in white dresses with blue satin sashes?’ I can see why we’re at this ball. Don’t any of these girls have unique color scheme? Does everyone still like that stupid musical?” She shook her head in disbelief. “Do we have anything to go on besides that this is a likely location?”

“We’re working on the assumption that the murder likes The Sound of Music, so those girls down there are both the likely victims and the suspects.”

Stein sighed in relief, “At least narrows it down a bit.”

Rogers nodded to the ball. “We’re in civilian clothes for a reason. Get mingling. Keep your eyes and ears open. There are other agents here, and hopefully someone sees something.”

Rick straightened his tie and started socializing with the fathers off to a side. He didn’t expect to find anything, but unlike his partner, he couldn’t exactly mingle with the youth on the dance floor. When possible, he steered the conversations to complaining about his imaginary daughter, to get the other men to agree and share their own stories. It was a long shot, but maybe he’d get some kind of clue to guide the investigation.

His hidden earpiece crackled, “Detective Rogers, it’s Stein. I’ve found something… suspicious in the kitchen. I need a second opinion before calling it in.” He almost pressed his lapel to reply, then caught himself. He had a lot of questions about how she’d gotten to the kitchen when she was supposed to be dancing, but he couldn’t ask in the crowd, and it’d probably be faster to just meet her than to find a private place to engage in ‘twenty questions’. He slipped away from his conversation as quickly as possible, and followed his memorized map to the servant areas of the mansion. Stein was crouched on the other side of a central island, and rose to when he entered, nodding towards the floor.

“See what I mean?”

“See what?” Rogers asked, walking around the island, “There had better be a very good reason you called me down he—” There was a dead debutante on the other side of the island, strangled with her own blue sash. He reached for his mic to call in the murder, but a sudden blow to the back of his head stunned him. When he started coming to, face up on the floor, Stein was pacing back and forth, muttering to herself. “Snow, snow, snow… It’s July! Where can I find snow…”

“Wh-, how-“ Rogers croaked, and Stein turned to him, a maniacal gleam in her eye.

“Flour will have to do.” She grabbed a handful and sprinkled it on his face, especially his nose and eyelashes. He tried to block her, but found that his hands were cuffed behind his back. Stein dragged the woman’s body into the kitchen’s walk-in freezer, then did the same with Rogers, ignoring his kicking.

“Why are you doing this?”

Stein looked at him, clearly offended. “I didn’t have a choice. I was trying to give every line its own murder, but the third verse is tricky, so I had to improvise. You and her are going to do double duty so I can cover white dresses, snowflakes on faces, and winter all at once.” She left and came back with a fire extinguisher, which she used to break off the inside handle on the freezer door. She ignored his shouting as she walked out, and she pleased to hear that the door muffled the noise. She wiped down the extinguisher to clean off her fingerprints, turned down the temperature on the freezer to make it quicker, and rejoined the party. After asking a nervous looking man for a dance, she continued scheming as he avoided talking to her and led her through the steps.

A dog-themed murder would be easy enough to set up, and for the bees she could find someone allergic. After that, she’d have to move on to a different musical. But which one? The dance music changed, and in a misguided effort to be hip, the band started playing Let it Go. Stein excused herself from the dance immediately and joined some other young women she suspected were FBI agents, to keep building her alibi. The music grated on her nerves, and she felt the urge to start on a new song early, but she forced herself to be calm. At least the next theme had been chosen. It was a slow way to go about it, but there would be no musicals by the time she was done.