Note: I love the Harley/Ivy pairing, and thought it might be interesting to write something more focused on the Joker's reaction to it.

The Joker was furiously pacing in his cell at Arkham, holding onto a handful of papers which he couldn't quite bring himself to look at yet. He narrowed his eyes as an image of Harley appeared in his mind.

So it's true, is it...?

Everyone had heard the rumours, of course. Harley and Poison Ivy were an item now – but Joker knew better. Harley was his. She always had been, ever since that fateful rose, and always would be. Once the Joker gets under your skin, you're never quite the same again, especially if you're a weak-willed, hopeless nutcase like Harley.

Harley had her charms though. She had looked after him well, he supposed, and was an acceptable sidekick. Even if she was clumsy and dimwitted at times, she was always so eager to please him; she did anything he asked her to, no questions asked. Which had been truly fantastic in the bedroom...

"Ugh, and to think people are saying she'd do those things for Pammie."

The papers crumpled in his hand. His knuckles were even whiter than usual as his ugly skin stretched over tight fists. The papers caught his attention again. He'd pulled a lot of strings on the outside to convince Harvey to get hold of these probably meaningless letters for him (probably meaningless, but he just had to be sure). He supposed he may as well read them, and settle the matter once and for all.

Harley belonged to him and only him. All these letters to Poison Ivy would contain is the kind of worthless drivel he never cared to listen to. So, what was he waiting for?

He opened the first letter, immediately recognising Harley's scrawl on the flowery writing paper. He began to read in a mocking voice.

Hey Red!

I feel a bit silly writing when we're in the same building and all, but getting only a few lousy hours of leisure time each day makes me awfully lonely. I can see the vegetables we planted through the bars of my window, and all I can think about is you, you, you.

Joker laughed. "Oh, Harley, you sound so pathetic! No wonder they've got you locked up with extra medication."

I'm glad you're here in Arkham, Ivy. I mean, I'm not glad Batman dragged you back in here, but at least we're together again. There are so many things about you I didn't realise I would miss until I found myself stuck in here alone. The way you make me smile, the happiness that bubbles up inside me every time I catch your eye... I even miss that look you get when you're mad or frustrated with me.

"Sentimental garbage." Joker waved a dismissive hand, but there was an uneasy feeling in his gut.

What I miss about you most, though – and don't you dare laugh at me, Red – is the nights we spent together. I'm getting all flustered now as I remember how you make me feel – even as I just lie next to you with your red hair tickling my face, drinking in your scent as your chest gently rises and falls with each breath. I wish I slept as well as you do. God knows I don't sleep here.

I want you here with me, Ivy. I want you to kiss my neck and make me squirm. I want to feel your warm, healing lips all over my poor unloved body. I want you to tease me until I can't take it any more. I want your strong fingers inside me, sliding over my clit and making me feel so good all I can do is scream. I want to tug at and tease the unruly hair between your legs, exploring with my fingers and kissing your most sensitive areas. I want you to do the same to me.

Most of all, I want to get the hell out of Arkham so we can be close again. Our restrained interactions here are painful. And you know what? I've gotten myself so worked up writing this letter I can feel myself throbbing... I'm aching for you, Red. Guess there's only one way to deal with that, huh? I hope you're thinking of me as you do the same...

All my love,

Harley.

Joker's voice was no longer mocking. It was shrill, disbelieving. Enraged, he scrambled to look through the other letters, and upon finding them all expressing similar sentiments yelled, "HARLEEEEY!"

He was banging on the door of his cell, shouting obscenities, describing how he was really going to get her this time... How dare she say such things to anyone else. Let alone Poison Ivy – of all people, what could Harley possibly see in that misanthropic plant lady? Sure, she had a reputation among the Arkham crowd, but where was her style? Where was her humour? He was rattling his door so loudly it sounded as though it might come off its hinges. Security guards came rushing over; he was forced into a straightjacket and fed a strong sedative.

Still, his outburst had been heard almost throughout the asylum. Poison Ivy listened eagerly, her lips twisted in a smug smile. Hearing that psychopath suffering gave her a warm, fuzzy feeling quite unlike anything else. He deserved to suffer, even more than the Bat, for the way he'd treated Harley.

"She's not yours now, you twisted bastard," murmured Ivy.

She would have to thank Harvey for his help. As much as it had pained her to give those beautiful, treasured letters to him, getting revenge on the Joker, however small or petty, made it all worthwhile.

It was just past two in the morning, and most of the inmates of Arkham were asleep. Joker was pacing again in his new cell in the isolation unit. At least here he could think without having to compete with Eddie's sleepy ramblings in one ear and Croc's snoring in the other.

Anger had given way to his special brand of cool, twisted logic. Harley would remember her place and come crawling back to him sooner or later, just as she always did. But it was what she did in the mean time that perturbed him, and who she did it with. Joker liked to think of himself as above jealousy, especially when it came to Harley. Oh, it was fine for her to cling to him, to stew in possessive jealousy every time he ignored her... He liked that. He liked watching her huge puppy-dog eyes beg him for forgiveness every time she screwed up (and boy did that girl screw up a lot) and her recklessly unquestioning devotion. It was endearing, but rather pathetic. And the Clown Prince of Crime was not pathetic.

"That's it!" He laughed maniacally. "I'll write some letters of my own. Oh Harley-girl, you're going to regret ever crossing the Joker! I'll sort out our little Pam problem once and for all..."

An unhinged laugh echoed through every corridor as he worked out the finer details of his plan. A few floors down, Harley tossed and turned and cried out in her sleep, as though somehow she knew he wanted to hurt her.