Casey did show up on shift the next morning. He'd gotten through the night without any further issues, all the same he was leery of eating anything and had only had two pieces of plain toast for breakfast and a cup of black coffee. He'd also, unbeknownst to anybody, shown up at 51 with a bottle of Pepto-Bismol in his bag that he stored in one of the drawers in his desk. After the morning brief he'd spotted a pink bakery box of doughnuts open in the common room, and he was half tempted to pick one up, they looked good, but his better judgment won out and he left them alone.

Less than an hour into shift, something happened. Otis, Cruz and Mouch all started complaining of feeling lousy, which soon gave way to nausea, and half of the Truck company was violently ill simultaneously, and very quickly after that, Capp and Tony were also doubled over puking their guts up. Casey watched this unfolding with a horrible sense of déjà vu, he looked at Severide and the two just watched all this with no idea what was going on.

Boden's attention was quickly drawn to the situation and he ordered everybody go to Med to get checked out and for Haz-Mat to come in and sweep the firehouse in an attempt to get to the bottom of it, and the health department as well.

Half an hour later at Med, Casey and Severide sat together in the waiting room, waiting to be examined everybody else, still trying to figure out what was going on.

"You ever get the flu in the middle of the day?" Casey asked out of nowhere.

"Huh?" Kelly turned to him.

"I was feeling like hell the other night...usually when I get the flu it doesn't really kick in until I wake up the next morning...I don't ever remember just getting sick in the middle of the day...and as far as I could tell, everybody else was fine when they walked in this morning...that's pretty quick to just get sick, isn't it?"

Kelly shrugged, "Never thought about it, I guess."

Casey pressed his fist against the side of his head and shook his head, "Something's not right, Kelly."

"What're you thinking, Matt?"

"I don't know..." Casey looked at him suspiciously, "how are you feeling?"

"Me?" Kelly shrugged again, "I feel fine."

"Guess that's something," Casey replied.

"Hazmat didn't find anything, neither did the health inspector," Herrmann said as everybody returned to the station house.

"And by the time everybody got to Med, there wasn't anything left for the doctors to test," Casey said, another surge of déjà vu coursing through him as he remembered throwing up until there wasn't anything left. He turned towards Kelly and said under his breath, "I told you."

"Told him what?" Herrmann asked.

Casey looked at Herrmann, and after a brief pause, answered, "I got sick two days ago, I told Severide if it's some kind of flu, and the rest of the house gets it, 51's going to have to close until further notice."

"This doesn't feel like any flu to me," Otis said as he sat down. "Feels like ptomaine poisoning."

"What's that?" Cruz asked.

"Food poisoning," Casey answered as an idea occurred to him and he headed to the kitchen.

"One form of it," Otis replied, "I got it once eating at one of those fried chicken restaurants, so did most of the other customers...turned out that night the fry vats were only operating at half the temperature they should've been, I was sick for a week."

"Well that can't be what-" Mouch made a gagging sound in the back of his throat and swallowed cautiously, "that can't be what this is, we didn't eat the same stuff."

"What about breakfast?" Otis replied.

"Hey, there wasn't anything wrong with it," Cruz told him, "I cooked it myself."

"You're not the best cook."

"Hey!" Herrmann broke it up, "don't start getting snippy, I feel like I'm at my in-laws' for dinner."

"It could've been breakfast," Otis said.

"Then how did Casey get sick two days ago?" Cruz replied.

"What happened to the doughnuts from this morning?" Casey asked as he returned to the room.

Otis groaned, "You actually thinking about eating?"

"No," Casey replied, "Who all ate them?"

Hands went up, Casey looked around and did a head count. Half the guys from Engine, most of the guys from Truck, and everybody on Squad had their hands raised.

"Can't be the doughnuts then," Otis said, "only half of the people who ate them got sick."

"But where are they?" Casey asked, "I can't find the box."

Nobody could answer that, the last anybody saw, they were on the table in the kitchen.

"Who brought them in?" Casey asked.

Nobody answered but everybody started looking around at everybody else, but nobody would take the claim for it. Casey looked around at all of them, and finally settled his eyes on Kelly, and asked rhetorically, "What the hell's going on?"

The next day Casey was still poring over the question of what made everybody sick when there was a knock at his door. He went to see who it was, and it turned out to be Severide, a huge Tupperware bowl of something in his hands.

"Hey, Cathy was sorry to hear you weren't feeling well the other day, so she made some soup."

"Oh..." Casey looked at the large bowl tinted red full of what he guessed to be chicken soup and forced out, "She really shouldn't have...did she make some for everybody else too?"

"For Otis, Cruz, and Capp anyway," he said as he entered the apartment and headed over to the kitchen.

Casey felt the wheels turning in his head. "The ones who came over for dinner."

"Yeah," Kelly said as he put the bowl on the counter, "she was worried that they might've gotten sick from something that she made that night...but that's impossible because they're the only ones that had dinner with us that night, and half the firehouse got sick yesterday."

Casey blinked, "And you ate the dinner, you didn't get sick...and you ate some of the doughnuts too...so that can't be it...there wasn't any one thing that all of us ate on the same day...so what could it be?"

"Who knows?" Kelly shrugged. "Maybe it is a stomach virus."

Kelly peeled the lid off the bowl, the plastic was nearly hot, and smelled the contents inside, yep, chicken soup, with, he looked in and tried to make out what was floating in it, thick homemade egg noodles.

"Have you tried any of this?" Casey asked.

Kelly shook his head.

Casey knew he was reaching, and he knew he should be ashamed of himself for even thinking of it. But he looked over at Severide and suggested, "Get a couple bowls and we'll both try it."

Kelly didn't have to be told twice. Casey dished up a piping hot bowl for both of them, it about burned his tongue and it was loaded with salt, but it tasted alright. But, as he looked over at Kelly, who had already inhaled most of the noodles from his, he knew that time would be the true factor that decided if it was alright or not.

He knew it sounded paranoid, and stupid, but he just couldn't shake the feeling that his illness wasn't just random. If there was any chance the soup had been spiked with something, then Severide would also be feeling the effects of it, and if not...then he was wrong and needed to pull himself together. But the truth was he felt better having somebody with him, who if any tampering had taken place, would also be feeling the effects of it before too long. Not that he would wish what he went through on Kelly or anybody else, but if he got sick too, it would be harder to brush off as mere coincidence.

And yet...if that were true, how could Casey account for anything? Five of them had eaten the dinner Cathy made, Casey was the only one who got sick afterwards. Nobody else from 51 got sick until 2 days later, much too long for it to be food poisoning from the dinner party. And had she had something to do with the doughnuts yesterday? Nobody could even answer who got the doughnuts, how they had gotten there, according to everybody it seemed that they were just there when they showed up. But that didn't make any sense either since there was always somebody at the fire house and somebody should've seen whoever brought the box in...unless it was somebody on First Watch, unless they were brought in before shift change. And if that was true, that left Cathy in the clear, but it still didn't make any sense.

But what did that prove either? Twice as many people had eaten the doughnuts than had gotten sick, and assuming they had been tampered with, it was impossible to know who would pick which ones, there would be no rhyme or reason to know who would get sick and who wouldn't. Just like dinner the other night. If Cathy had dished up the plates for everybody herself, that might suggest she could've tampered with Casey's...but that's not what happened, everybody dished up their own food, and again, it would've been impossible to know who would pick what, or how much, it would've been impossible to know that Casey would be at the end of the line and wouldn't get his plate until half the food was already gone.

Casey shook his head and wanted to kick himself. He was being paranoid. They were exposed to hundreds of germs a day from the people they encountered on calls, it could very well be the flu or some other virus that was working its way through the Chicago population right now.

You're being paranoid, he told himself. It was just a stomach bug, he kept reminding himself.

The next day Casey had gotten a call from Chicago Med about the blood and urine tests they'd run the day everybody came in, and Will Halstead had requested he come down in person to hear the news of their findings.

Casey was already sitting in a chair when Will told him, if he hadn't been, he surely would've collapsed on the floor in disbelief. Instead he gripped the arms of the chair as if he was holding on for his very life.

"This can't be right," he said, "there has to be some mistake."

"Now there's no need to panic, Matt," Will assured him, "there are a lot of ways a person can be exposed to arsenic and not realize it."

Casey shook his head, "No...the test has to be wrong."

"Have you responded to any calls lately at glass factories, wood treatment plants, any place that manufactures or uses pesticides?"

"No...I don't think so...I don't know," Casey was just about beyond the ability to even think.

"Do you eat a lot of rice?"

"Not really, why?"

"It's full of arsenic...in moderation it shouldn't be anything to worry about, but we know that's not a word most people are familiar with these days."

Casey tried to make sense of what he was hearing. "Why is rice full of arsenic?"

"There's a lot of arsenic in the ground water, it also dissolves off rocks and from the soil, and can all be taken in by the crops," Will said. "And as far as the ground water's concerned, what's already naturally occurring is one thing, there's another issue of the old cemeteries around here."

Casey looked at him and raised an eyebrow, "Why?"

"It wasn't uncommon for arsenic to be used for embalming in the early 20th century, that would already leak into the ground water, but as much rain as we've been getting lately it's not impossible that some of the old graves got flooded and washed the rest of the arsenic down into the city water. But all of those would've been more gradual buildups and you likely wouldn't have experienced any symptoms from it. Since we already know you tested positive for arsenic, what I would like to do is run a hair and fingernail test to give us a better idea of how long you've been exposed."

Casey looked down at his short nails he kept clipped close to the brim and told Will, "I don't think you'll be able to find much."

"We can get a better idea testing your hair," Will said.

"Is...is...I mean...what happens now?" Casey asked.

"If you haven't been exposed long then there shouldn't be much to worry about, if we can find out how you were exposed and cut off that source, you'll be fine," Will told him.

Casey finally thought of something. "What about everybody else? Did their tests come back with arsenic too?"

Will looked at him and answered, "No."

Casey felt his hands shaking and the muscles in his arms clenching as he walked up the steps to Severide's door. He didn't really remember leaving the hospital and driving over here, and he didn't feel in any condition to drive back to his own apartment anytime soon, so he hoped Kelly didn't mind having the company. He knocked on the door and anxiously waited.

He heard the locks being undone, the door opened and this time it was Kelly standing there. "Casey, what's up?"

"Can I come in?"

Kelly held the door wide, "Yeah, sure, what's on your mind?"

"Uh...I've got...I got some news..." Casey found himself pacing around the living room, "and I don't...uh...how are you doing? Have you been sick?"

Kelly shook his head, "No, I'm fine. What's wrong?"

"Will called me...he said...they found something in the blood test they took...he thinks it's why I got sick."

"Well that's good, isn't it?" At the look Casey shot him, Kelly elaborated, "I mean if they know what it is they can treat you for it, right?"

"I hope so," Casey felt his legs getting weak and shaky, "Uh...I..."

"You better sit down before you fall down, Casey," Kelly said as he lightly nudged Matt over to the couch, "now what's the matter?"

"Uh...Will said that...they found...I have..."

"Kelly, who's here?"

Casey all but jumped at the sound of Cathy's voice, he turned and saw her coming out of the kitchen.

"Oh, hi, Matt," she said, "I just got dinner ready, you want to join us?"

"Uh, no," he said as he forced himself to his feet, "I have to get going."

"Whoa, wait a minute, Casey," Kelly grabbed him by the arm, "what did the doctor say?"

Casey turned back towards him, and not turning his head, merely moving his eyes to look through the corners of them, he looked at Cathy, who stood in the middle of the room looking at him, no readable emotions whatsoever, but suspecting she too was waiting to hear his announcement.

"He...uh...said it was food poisoning..." a news story he'd seen earlier that week came to him and he added, "he said there's been a recall of frozen meat for possible E. coli...thinks that's what it was."

"Well that's got to be a relief to at least know what caused it," Kelly said.

"Uh...yeah...I'm sorry to barge in, I just thought I'd tell you...did you get your tests back yet?"

Kelly shook his head. "Haven't heard anything."

Casey nodded his head, "Probably nothing then...I've got to go..." he turned and headed for the door, but looked over his shoulder back to the blonde woman in the room and said on his way out, "Thanks again for the soup."

He closed the door behind him, and all but ran down the steps towards his truck. Once at the curb, he kicked himself for the way he'd just acted. What the hell was wrong with him? Arsenic, he had arsenic poisoning, why was that so hard to tell Kelly once he realized Cathy was in the room? If he was the only one who tested positive then that proved she couldn't have had anything to do with it. But then where did he get it? And how long had he been exposed and not known it?

"Hair doesn't lie, Matt," Will told him the next time he came in, "you've had a sizable amount of arsenic in your system less than a month."

"You can tell that?" Casey asked.

"Drugs, chemicals, metals, they store up in the hair just like the rest of the body, we average one inch of growth per month, got a sample approximately three inches in length, only the newest growth contains arsenic. So it's obviously very recent."

"Could it have been something I ate?" Casey asked.

"Well if I had to guess I would wager you consumed the amount instead of just absorbing it through the skin. And an amount like this, you would've gotten sick fairly quickly after eating it," Will said. "Does anything come to mind?"

Casey shook his head. "Not really." The last thing he needed was Halstead also thinking he was going nuts. "But if...if I get sick again, can I come back and..."

"We'll run the test again and if you get here when you first get sick we can check your stomach contents," Will told him. "You really should've come here the first night, Matt."

"I know, but I just thought it was the flu."

"People come here for flu all the time," Will pointed out.

"Yeah, and it annoys the hell out of everybody working here," Casey replied.

Half of Will's mouth turned upward in an amused smirk, "Not exactly, in any case, if you'd come in here as sick as you were, that would've fallen under 'acceptable flu cases'." A small laugh escaped him.

"Did you find out what made everybody else sick?" Casey asked.

"Sorry, Matt, patient privacy laws, you know that."

"But you're sure they don't have it too?"

Will merely nodded in response, as usual at least one toe over the line of what was appropriate practice as a doctor.

Casey didn't have any idea what it all meant, but he didn't like it.