A good detective story should have an interesting and complex mystery at its core. This keeps the readers guessing. Also, a memorable detective character is crucial. The detective should be intelligent, observant and have a unique personality. Another element is the setting. It should be vividly described and sometimes contribute to the mystery, like a spooky old mansion.
The elements of a good detective story include a diverse cast of characters. Besides the detective, there should be suspects with their own motives and secrets. The pacing is important too. It shouldn't be too slow that the reader gets bored or too fast that the details are overlooked. And the writing style should be engaging, drawing the reader into the world of the mystery, making them feel like they are right there with the detective, trying to solve the case.