So here's an idea that popped into my head in how Danny found his own connection to Lindsay's friend Lucy. Takes place between seasons 4 and 5.

It was a rare evening off from the lab. Danny walked down the street with Lindsay at his side, full from dinner and dealing with the nagging worry. They were finally back on even ground. There was finally a mischievous glint back in those rich brown eyes.

But he'd done something very, very bad.

Something she might literally kill him over.

And she knew how to hide evidence.

"Okay, you might as well tell me," Lindsay said suddenly, without looking at him.

"Tell you what?"

"Whatever it is that's making you breath that way. Come on, Danny... you've been tense all night."

He let out a breath. "Fine. You know you kind of left you're diary at my apartment for a few weeks."

"I don't have a diary." She stopped in the middle of the sidewalk and looked at him, however, as recognition dawned.

"Yeah. More like letters."

"You read them?"

"Well, I..."

"Danny, those were private thoughts." Her eyes grew wide as she realized just what he'd read. "Private words that were only meant to be between me and my friend. You don't ... eavesdrop on private conversations."

And she was mad. He'd known she would be, but he also knew he didn't want anything between them.

"I missed you."

"That isn't an excuse. I was a phone call away."

"You know I couldn't call. I couldn't ... it should count that I needed you."

"But you couldn't tell me. You couldn't ask me. You couldn't be with me."

She spun on her heal and walked away from him.

Danny let out a breath and followed. He gave her space. He knew she would need it. The thoughts were steam rolling through her mind.

Lindsay was private. She didn't tend to talk about her feelings, except she'd started to do so with him and, he knew now, to her long ago deceased friend named Lucy.

The journal ... or rather book of letters had begun simply.

Its been a long time since I've written to you, but that doesn't mean I haven't thought about you. Every moment of every day since I moved to New York three months ago I've had dozens of things to tell you. New York is magical. Of course, we had that conversation before. Living here is magical too. It is everything you would have wanted it to be. I wish you were here.

She'd gone on to detail her ghost tour through the city, or rather five different ghost tours she'd been on in those first few months. She'd been lonely, he'd realized, and home sick.

There were comments about Mac and Hawkes, Don and Stella. There were also her thoughts on him. He was fairly sure it was those thoughts that upset her the most.

Even as he'd read the words he understood that part of her, at least, was describing him to a fourteen year old friend.

Still, it had twisted a knife in his gut when she'd said, over and over and in different ways, through those letters over the last two years, that she would have liked him. She'd detailed her crush in such terms, and then the trial.

He wished he'd been there for her, because as the letters went on and as they grew closer Lindsay had admitted that she could talk to him as she could to Lucy.

Lucy.

He felt such a connection with the young girl from Lindsay's past, and in many ways, he owed Lucy for brining Lindsay to him.

It had been Lucy's desire that had changed Lindsay.

He couldn't—for himself, for Lindsay, and for Lucy—mess this up.

Again.

"Lindsay."

He picked up his pace and chased her down.

"I'm sorry. I only told you now because I nearly said something out loud the other day that I learned from those letters."

"That's not an excuse, Danny."

"No," he grabbed her arm and pulled her to a stop. "It's an apology. Lindsay ... I wish I could have known her. I wish I would have been there for you those first few months in New York. I wish—"

"You were."

"I was what?"

"You were there for me. You and Don. We went out, dozens of times. We played pool. We had bears and watched football."

"But you couldn't talk to anyone like her."

"That was private."

"Until you could talk to me."

"That was private, too."

"I know."

"And not ... particularly accurate. Danny, I say things to Lucy that I learned not to say to others. To my therapist. To a witness. To people in town. I ... maybe I was saying those things to you. I don't know."

"I'm sorry I hurt you. I'm sorry I read those words. Sort of."

"That helps."

"She was your best friend. She's part of you. You've only really told me the barest things about her, or about any of them. When you're ready, I want you to tell me about her. About them, if you can."

"I don't know if I'll ever be ready."

"Then just tell me one thing. Just one thing about Lucy."

"You're the one who read something private. How did this get turned around on me?"

"Just tell me one thing."

Lindsay slowly licked her lips, then sighed before closing her eyes as if she had to dive into deep memories.

"We were all going to college together. We promised each other that. But Lucy had these prints on her walls of great big cities. London. Paris. Jerusalem. Moscow. New York. She loved details. She wanted to be an architect. She was going to come to New York one day. She was going to be an architect of big beautiful buildings. I never saw myself in New York, until all I could see was Lucy right here. I wanted to be here, where she wanted to be ... and later, I wanted to be here for me."

For a moment Danny let the words settle, then he turned and opened his messenger bag and pulled out a wrapped package that could only be another journal. He'd seen it in a shop window a week ago, and known the embossed cover of the New York skyline was perfect.

"Just one more thing," he said as he handed it to her. "If you don't want to do this, I understand, but I'd like you to let me keep the journal I read."

"Danny—"

"No, just hear me out. I promise not to read any more of your ... letters. I promise never to invade your privacy that way. I don't want you to stop writing when you need to, but I'd like you to let me have the one I read. I'd like to keep it."

"Why?"

Because I...

"Because giving it up feels a little like giving you up."

For a moment Lindsay stared at him before she turned and started to walk. "I can't believe you've turned this around so that you want me to give it to you now. Danny, you're the one who read it without permission. I never should have taken it there. I never should have ..."

"Lindsay."

"Did you even think?" In the middle of the sidewalk, she spin on him again. "Did you even stop and think how humiliating this would be for me?"

"No. Not when I picked it up and started to read." Danny reached out, ran his hands down her forearms to steady her. "But I understand a lot now. I know why walking in the rain is something you need to do. I wouldn't have known—"

She turned and started to walk again.

"Lindsay, I wouldn't have known that walking in the rain makes you feel like Lucy is by your side, because you can't talk in a good downpour, so you can pretend."

"I never said that." When she looked at him there were tears in her eyes, and she never cried. "I've never put that into words."

"No, but you talked about walking in the rain here, in New York."

It rained today.

"Lindsay, you just need to know that those letters mean the world to me. If you can't let me hold onto it, just that one, at least think about forgiving me."

She shook her head and started to walk again. This time, he left her alone. He let her walk and think. They moved down three blocks until they were back at the stoop in front of her place.

There she turned, her look a little softer, her eyes less haunted.

"I don't know if it's a blessing or not, because I don't know if I ever would have told you, or could have told you those tings about Lucy." She looked down at the new wrapped journal in her hands and sighed. "But suddenly, there are dozens of things I want to tell you. Just ... let me have this, with her. It's all I have left."

"No. You have a lot left of Lucy," Danny leaned close and kissed her forehead gently. "She's inside of you, Lindsay. She's part of who you are now, otherwise, the letters wouldn't mean so much to you ... or me."

"You're still in trouble you know," Lindsay said, but there was a smile in her eyes she couldn't quite hide.

He grinned. "How much trouble?"

"More than that smile's going to get you."

As she turned and headed up the stoop, he followed. "You sure about that, Montana?"

And later, as they laughed ... you fill in the blanks.