Okay, so it wasn't a ghost. As the hare explained as he let Judy and Nick into the small house (which Nick noted was absolutely freezing) he was Christopher Whitepaw, Trent's twin brother, who had left Zootopia years ago. He'd only come back on Trent's request recently.

"So…" Christopher began as they all were seated at a coffee table, "What kind of trouble is my brother in? Of the two of us, he was always the least reasonable."

Judy met Nick's eyes, both looking sad at Chris's behalf. "I'm… Sorry Mr Whitepaw, but… Trent was found in Tundra Town last night. He's dead."

There was a long period of silence as Christopher slowly absorbed the information. "Oh… Oh…" He finally manages. "I guess I should have seen this coming, he always got in trouble. I just… I thought he finally turned a new leaf. He had me come down here just to keep the place presentable, said he was finally going to find someone to buy it."

Judy let Christopher have a moment before pulling out the key Tuskton had given her. "This was found hidden in your brother's things, did you know where it goes?" She asked. Christopher took the key, staring at it for a moment. "The only lock it could fit would be the one for the basement I guess, Trent did all of his work there. I'll unlock it for you."

The trio walk further into the house, Chris stopping at a door with a simple, old fashioned bronze lock. Chris unlocked the door, and pushed it open. Down below was a dimly lit cellar, reeking of the smell of rot and dying plants. All three mammals covered their offended noses. "Oh Trent what did you keep down there?!" Chris wondered aloud.

Nick, being the only one with above average night vision, surprising considering all of the carrots the other two eat, was the first one headed down. Down below was a series of of lab-like equipment and blooming blue flowers, but unlike what one would expect, these ones were rotting and diseased. A small, black died diary like book was laying on the table next to the flowers. "How long has he been gone?" Nick asked, as he picked up the diary, flipping through the pages. It was full of long winded, formulaic analyses of the Nighthowlers, so naturally, Nick couldn't make heads or tails of it.

"Less than a day." Chris noted, looking around the room. "Granted, I don't think he was down here at all yesterday."

Nick reached the back of the diary, to his surprise finding a page addressed to Christopher. "Hey, come take a look at this." He said, motioning the two lapines over to him. The page read like a letter…

To my brother Christopher,

If you're reading this, chances are I'm either dead or missing. Or you broke into the basement while I was out, but that's more something I would do. I suppose you deserve some explanation for what's going on. About a month ago, I was contacted by an organization that was interested in my one area of expertise, plants. Specifically, illegal plants.

Judy gave Chris a look. The white hare shrugged. "I just thought it was a good thing for him to take up gardening, I didn't know he'd start growing drugs."

Nick rolled his eyes and continued reading.

At first, I was more than happy to help out. These Nighthowler flowers are harmless as long as they are not ingested and the liquid made from them is safe as long as it's not touched so I was in no danger during my tests, but overtime the requests of my employers became strange. They had me introduce a strange fluid recently, and the results of that are obvious. The flowers began to wilt and decay, regardless of my efforts to keep them alive. However, they still could be distilled into a similar fluid to the results, but when heated they form into a gas. I don't want to know what my employers have in mind for this, but I doubt any good will come from it. Chris, I know you have no attachment to Zootopia, but I've left you something that might convince you to help stop this, just open the drawer below the flowers.

Chris didn't even resist pulling the drawer open. It was empty, but upon opening it, there was a click as a burner on the other side of the room turned on, heating up a flask filled with a dark blue liquid.