I don't own Castle and never will. No copyright infringement intended.
Author's Note:This is based on my most likely completely dead wrong theory that Castle and Beckett will marry before he "dies". Hope you enjoy!
Kate actually came up with the idea, surprising both of them. Urging Castle to rest (he was refusing to listen, despite the pain he was in), she gasped when the idea hit her. "What?" he questioned.
"Let's get married now, Castle."
His mouth dropped open and he gaped at her. "Now?"
She nodded. "I love you and despite the fact that I know we're going to find the antidote, I want to be your wife."
"And you're not just saying this because you're scared we won't find the antidote?" He didn't want her to regret this once this situation was (hopefully) resolved and to end up resenting him. They hadn't even talked about their fight yet. The fact that he was dying (and fuck, that was a kick in the pants) had taken priority.
"Castle, no. I love you and whatever stupid issues we have can be fixed. You proposed to me and now I want to make it official."
He wanted to go on a spiel about her taking his last name and becoming Kate Castle, but he doesn't have the energy. This dying thing is taking a lot out of him. "Sure, let's do it."
Kate beamed. "Great. I'm sure we can find someone while they look for the antidote." She'd help once they found a justice of the peace or something and got married.
Castle leaned on her and groaned as the pain amped up again. He had called his mother and Alexis (which had scared the shit out of them, but they had both elected to be positive about finding the antidote) to inform them of the situation, but everyone else in the dark. Well, they probably knew now, but he honestly didn't care. He righted himself and tried to appear strong to his fiancée (she didn't buy it). "Let's go do this!"
With the help of her co-workers, the marriage license was approved faster than it legally should have been, but extenuating circumstances helped a lot. Rachel temporarily handed off the search for an antidote to another co-worker and stood in as a witness.
"Can you please hurry up?" Kate asked the justice of the peace. She was panicking about Castle because her fiancé kept getting worse and worse by the minute. She needed him to relax, but knew that wasn't going to happen. He had insisted on going along and put his foot down.
"Of course." The justice of the peace began his spiel. At one point, Rachel had to start physically holding Castle's back to keep him upright.
Castle and Beckett exchanged some short vows (he had to stop several times because he had no energy to do anything) and took the (plastic, which would be exchanged for something at the jewelry store soon, if he survived this) rings and slid them on each other's fingers.
"Glad you're my wife," he mumbled.
"And I'm glad you're my husband." She laughed at the look of delight on his face just as the justice of the peace told them they could kiss for the first time as husband and wife.
Not willing to hurt him any further, the two regretfully skipped that step and then headed out with the rest of the force.
"Should I be calling you Agent Castle now?" Rachel questioned.
Kate shrugged. "I think I'm going to keep my last name. Or I'll be Beckett-Castle. Been going back and forth on that and I haven't decided yet." She stroked her husband's hair as he leaned into her so he wouldn't collapse.
"Beckett-Castle sounds good," Castle murmured.
"Conserve your energy, okay? You don't sound good." Or look good, but she wasn't about to tell him that.
"Okay." He stumbled, but Kate's grip on him kept Castle on his feet.
She reluctantly left him in the car and expected him to follow, but surprisingly, he did not. And Kate definitely did not freak out when they returned and his eyes were closed (Rachel knew otherwise, but promised not to say anything since she knew how worried Kate was), no matter what anyone said. "You doing okay?"
Castle nodded and immediately wished he hadn't. Everything hurt now. If he survived this (the only reason he was staying positive was for Kate's sake and everyone saw it but her), he hoped he never went through something like this again. This was the most pain he had ever been in to and nothing would ever compare to it. "I'm fine," he lied.
Kate didn't buy it, but didn't say anything because she didn't want to contradict him, especially when he was dying. "Good, I'm glad. We'll be finding that antidote for you soon so don't you fucking dare give up on me."
He opened his eyes and stared at her. "I won't give up." Castle was desperately trying not to, but it wasn't that easy.
Fortunately for them, the antidote was found about two hours later. Castle was worse now and on the verge of dying (and should have been in the hospital, but he refused to go) so they had found it just in the nick of time. They administered it to him and hoped it wasn't too late. They waited impatiently.
Castle passed out in less than five minutes and Kate waited by his bedside, refusing to leave him. Rachel and the others left them alone so they could have privacy just in case it didn't work and the worst happened.
Kate noticed his color was starting to get better, despite the little whimpers he emitted in his sleep, but she shook from fear. She refused to let herself cry until she knew Castle was going to be okay (and that's exactly what happened later when everything finally caught up to her). When he finally opened his eyes a few hours later, she gasped in relief. "Kate? Have you been here the whole time?" He wasn't one hundred percent yet (and wouldn't be for a few more days), but he had more energy now than he did before.
She nodded. "Don't you ever scare me like that again."
He smiled at his wife and squeezed her hand. "I don't plan on it. Love you, Mrs. Castle-Beckett."
Kate beamed at the use of the name. "And I love you too. Now get some sleep."
"But that's all I've done," he complained before he was pulled under again.
Kate and Castle would have to deal with the wrath of getting married without their family and friends, but they'd renew their vows (with actual rings this time) on their anniversary with everyone present (including their surprise – not yet known about by anyone - guest). They were glad they had decided to marry when they did and didn't regret their decision. They had immediately fixed what they fought about before everything that happened and were able to make their relationship and her new job work. Castle nearly dying had been a blessing in disguise, but something they didn't want to repeat.