Detective Peter Pux sat at his desk, staring at the list of names in front of him. He had been working with Detective Sarah Smith for hours, trying to track down the middleman who had arranged the theft of the Mona Lisa.

"There has to be a connection here somewhere," Peter said, frowning. "But I just can't see it."

Sarah nodded. "I know what you mean," she said. "We've gone through every lead we have, and we still don't have a solid suspect."

Just as they were about to give up for the day, Peter's phone rang. It was a colleague from another department.

"Peter, I think I might have something for you," the colleague said. "I was going through some old files, and I came across a case that might be related to your Mona Lisa investigation."

Peter's ears perked up. "What is it?" he asked.

"It's a case from a few years ago," the colleague said. "We arrested a man for running a high-end art theft ring. He went by the name of 'The Middleman.' Sound familiar?"

Peter's heart skipped a beat. "Yes, that could be him," he said. "Do you know where he is now?"

"He's currently serving a prison sentence for his crimes," the colleague said. "But I think he might be willing to make a deal if you can offer him something in exchange for information on the Mona Lisa theft."

Peter nodded. "We'll be there as soon as we can," he said, hanging up the phone.

"We might finally be getting somewhere," he said to Sarah. "Let's go talk to The Middleman and see what he knows."

With that, Peter and Sarah set off to visit the prison and see if The Middleman had any information that could help them solve the case.