it's december 24th and their day starts off normal, just like any other day.

it was cold and snowing and hailey had never hated chicago more than she did in that moment (but it's her home; she wouldn't ever give it up). she beat jay into the office (she's usually the first one, being an early bird and all), but he showed up with coffee and a smug smile. their downtime doesn't last long, as voight assigns them to chase down a lead on their double homicide. this particular case had been dragging on with few breakthroughs and they were getting ready to ship it off to homicide, but voight wanted to take one last crack at it.

hailey leaned against the far wall while jay knocked on the apartment door. "william bradford, open up; chicago pd."

they hear nothing but silence and jay rolled his eyes, repeating his earlier words.

"another dead end," hailey mumbled, grabbing her phone to update voight.

jay nearly followed her lead and turned around but a noise from inside the apartment stopped him. "wait, did you hear that?" he turned to look at hailey and placed his ear against the door.

"no?" hailey looked confused.

"i heard something. it sounded like…" he knew it sounded farfetched, but he swore he heard a cry. with his ear up against the door, he's able to hear more cries; he swallowed harshly at the familiarity of a baby's cries.

from her new position closer to her partner, hailey clearly heard the baby's cries. "jay, does that sound like a baby to you?"

jay doesn't bother answering her; he moved back and sturdily kicked the door down. that's usually one of his favourite parts of the job, but he can hardly focus on that as the baby's cries multiply. hailey pushed past him and headed in the direction of the screams; it lead them to a dark bedroom in the back of the apartment. upon entering, they find a beautiful baby boy, who looked no more than a year old, lying in her crib with a red face from screaming.

jay is momentarily frozen because this young, defenseless child is here all alone, but hailey moved into action. she scooped the baby into her arms and cradled him against her chest, whispering soothing nothings against the baby's head. it took a moment but the baby's cries subside into whimpers.

hailey turned to look at jay with wide, watery eyes. "jay," she started to speak, but her voice broke. she wanted to say more but she can't; there's something about cases involving children that affects them all deeply, on another level. they are innocent and defenseless, and hailey is still stunned someone would leave a baby all alone like this.

jay doesn't need hailey to explain; he understood. he dropped an arm around her shoulder and held her for a moment as she held the baby who is now staring up at her with a transfixed expression.

"come on," he murmured, pulling her elbow gently. "let's stop at the hospital and will can make sure he's okay."

voight decided to meet them at the hospital. after hearing what his detectives found in the apartment, he couldn't not go out and make sure the little guy was alright.

"talk to me," he directed his words at jay, who is casually leaning against the wall. hailey is peaking through the doors, watching carefully as will examines their newfound baby.

jay snapped out of his thoughts quickly. "we knocked twice; nothing. i heard crying so we made entry. found the baby in his crib, unharmed and no sign of any guardian around."

"any id on the mother?"

jay frowned. "not yet. i have ruzek looking into it."

voight nodded. "alright, we're kicking this case off to homicide; too many dead ends. merry christmas, halstead," he smirked.

"sarge—" jay is on high alert, prepared to protest.

of course voight was expecting it; he knew exactly who his detectives were. "i want you to stay with this baby until we figure out who he belongs too." jay's eyes widen; he loved kids, but babies are incredibly fragile and a massive responsibility. "upton; you too."

hailey snapped her eyes to voight as if she hadn't been eavesdropping their entire conversation. "want us to call dcfs?"

voight paused, looking through the glass doors at will, who is finishing up with his examination and smiling at the little guy. "tomorrow is christmas eve," he replied gruffly, "i'm not letting that baby spend it's first christmas at family services."

he turns to leave, but jay and hailey are still confused. "wait, then where are we taking it?"

voight smirked. "you two found him; he's your responsibility now until you find the mother."

"what?" jay stammered, his eyes widening at voight's demand.

"you better hope ruzek pulls through and finds that mother," voight remarked in response, already halfway out the door.

before either have a chance to properly process what voight said, will knocked on the glass sliding door and motioned them inside. "find a name for this little guy yet?" will queried, as he picked up the baby from the checkup table.

"we have literally no information," hailey replied sadly, "don't even know who the mother is yet."

will frowned as he bounced the baby on his hip. "well, on the bright side, the baby is perfectly healthy. a little malnourished, but nothing some formula can't fix. do we need to call family services?"

"uh," jay scratched the back of his head, "voight told us not to actually."

"since we found him, he's our responsibility until we find the mother," hailey added, watching will's amused face. "he doesn't want the baby's first christmas to be at family services."

will can't help but laugh out loud; the baby in his arms giggled in response. "i'm sorry, but voight put you in charge of this baby?" he directed his sassy remark at jay, who looked offended. "is he aware that is the worst idea he's ever had?"

"i've dealt with babies before, will," jay rolled his eyes, but he really is nervous to handle a baby on his own.

will nodded, snickering as he passed the baby onto hailey. "oh yeah, sure, my bad. because we've had so many children in the family."

"shut up," jay groaned. "plus, i have hailey. she has nephews."

hailey nodded. the baby is calm, sleepy and slowly dozing off. "yeah, i do. i've babysat them many times."

"have you ever babysat them overnight?" will inclined with a raised eyebrow.

hailey's lips formed an o. "no…" she noted warily. "how bad can it be?"

will is so amused, he can't stop himself from bursting out laughing. "oh, you two; so unbelievably naive."

"stop being an ass and promise me you're coming over later," jay snapped, but his green eyes are pleading. if anyone can take care of a baby healthily, it's his attending physician older brother (even if he will tease jay about this for the remainder of their days).

will laughed and knocked jay on the shoulder. "yeah, i'll be there. but until then, good luck you two!" he sent them a cheery smile before exiting the room (a little too happily, if you ask jay).

the baby in hailey's arms was fully asleep now; she raised an eyebrow at jay. "your place?" he just stared at her in response.

"well, your house has stairs," he deadpanned. "stairs are bad for the baby."

hailey bit her lip in amusement. "stairs are bad for the baby that can't walk?"

"you never know," he rolled his eyes. "and in case it wasn't clear enough, you're spending the night at my place."

"how can i say no to such an inviting offer?" she replied sarcastically, but jay was so done with will and hailey's teasing. "oh relax," she answered (she can read him so well). "we have to pick a name."

jay's eyebrows furrowed together. "what are you talking about? his name is jay."

hailey rolled her eyes, and if her hands weren't full, she would have smacked him. "that's cute, but no."

"i actually had a better idea," jay noted, scratching the back of his neck nervously. "i was thinking alvin? i don't know; it might be too much, but it was just a thought."

hailey's heart felt like it swelled three times its size. "jay," she breathed softly, "it's perfect."

he smiled warmly. "okay, great."

"do you think will has an extra car seat or supplies? we have to stop by the district first," she expertly doesn't mention how kim and vanessa keep blowing up their group chat with requests to see the baby. "also, even though voight says this is our responsibility, i'm not sure if that means we don't have to finish our work day."

jay shot her a questioning expression. "i'm sure he's still expecting us," he grieved in response to the second part of her statement. "and i'm pretty sure they have some supplies in storage, unfortunately."

he knew enough from what will had said in the past that parents who lost their newborn babies in the hospital sometimes don't want to take their things home because the pain is too much. so they leave them at the hospital and it gets recycled to other moms who aren't as fortunate to buy such products.

"you good?" he prodded, his eyes flickering down to alvin sleeping peacefully. "i can go find will and meet you at the truck?"

hailey nodded. "yeah, that sounds good."

she watched as jay walked away in search of his redheaded brother.

"and so our adventure begins."

OKAY SO

if any of you watch ncis, you will recognize this as the plot from one of the episodes with ellie & nick!

i always thought it was absolutely adorable (so are they tbh) and always wanted to make it into an upstead theme... so, here it is, i'm trying lol

i think it's too much to just fit in a one-shot so i'm going to make it multi-chaptered! definitely two chapters, maybe even three, depending how it goes.

hopefully you guys actually like this idea lol... let me know! i realize this chapter was kind of bland but it was just the set-up i needed to get started! next chapter will include the whole unit with endless teasing and fluff.. so stay tuned!

and as usual, any prompt or requests or ANYTHING, please drop a comment below bc i'm always looking for more ideas on what to write!

thanks everyone, enjoy & stay safe xx