TOC page here.
So we hit the climax of the last scene, where everyone has had their eyes opened—maybe even Lieutenant Dave. Nobody is who they seem, and Rosa wasn’t Rosa. So let’s replace the illusion with the truth through dialogue:
“Hey, listen; this was a lot of fun. It really broadened my horizons.” He took a key ring from a white plastic shopping bag that lay on the floor near the bed.
“Great,” said Rosa. Once he had released her, she stretched, stood up and put on a black silk kimono. “Glad I could be of service. So what happened to Alex?”
“Honey,” said Littleton, “these two are the senior Homicide detectives.”
“Oh, shit; Alex is dead?”
“I’m afraid so,” said Diana. “And my partner is the senior Homicide detective; I’m way down the totem pole.”
Littleton shook his head. “What I hear, he wouldn’t eat if it weren’t for you.”
“You mean I wouldn’t stop eating,” said Mustapha. “Ms. Pinelli, your friend Alex was murdered about the time you were driving to Starship. If you’ve got a receipt in that bag, I could help you both out.”
“Yeah, it’s right here; do you want the dinner receipts, also? Why would anyone – oh, you’re here because you think I’m a suspect.”
“That’s right, ma’am,” said Diana. “Some of Alex’s friends told us that you had been seeing each other.”
“Yeah, but I tossed him to the curb maybe two weeks ago. He’s a nice guy, and he had some pretty nice equipment, but he couldn’t use it, especially once he was half full of cheap bourbon.”
“Sorry to hear that,” said Mustapha. “His buddies said you had an ex that was giving you trouble?”
“Ricky, you mean? He’s all bark and no bite; besides, it was when he went to jail that I figured I could get rid of Alex and not have to worry.” She blushed, for the first time since Diana had opened the door. “I mean, get rid of him as in break up with him. I didn’t kill him. I liked him, really: it was just the whiskey dick I couldn’t deal with. Those guys he hung out with, you might want to start looking there. Some of them are alright, but most of them are nothing but trouble.”
“That’s the problem, ma’am,” said Mustapha.
She didn’t do it: she has a receipt from the sex toy store. What clearer alibi could you want? So apparently here, they’re at a dead end; but they’re not, because someone posed as Rosa. But Diana and Mustapha still haven’t raised this with each other. Only if you paid attention to what Mario said are you going to have already figured out someone was posing as Rosa. Now, it’s confirmed. So there’s fun for the reader in a well-constructed piece of dialogue, because they already know before Rosa confirms it that someone else took Rosa’s place. They’re reading a detective novel, after all.