They've been at each other's throats for days now. His temper a furious, raging, biting thing that has bounced and echoed endlessly through the concrete landscape of their underground working environment. And she has been right there with him, toe to toe, and just as defiantly stubborn, her sharp claws gleaming in the harsh glare of artificial lighting. Any opportunity given by one and the other immediately rises to it, meeting the challenge with a shower of sparks and a clash of persistent determination.

They are unwavering in their defense of their respective positions, and the more this case has dragged on, the more unyielding and inflexible they have become. The tension is firmly wrapped around them both; like wildcats they are poised to strike at any moment, at any weakness. They are both right, they are both wrong and neither will admit it. The middle ground is constantly in flux as they push and pull each other, each intent on having the last word, neither willing to make that first compromise.

The breakthrough comes with an unexpected confession, and they are both temporarily stunned into silence. They share an intense and lingering stare down, silently acknowledging too many things and it goes the same way as their ongoing argument; neither is willing to look away first. They've been here so many times before it's verging on the ridiculous.

Incredibly though, in the end, he offers the olive branch first. He smiles at her, and it's that devilish, heart-stopping grin that she is just far, far too fond of. He's apologetic, understanding and still her best friend. She holds his gaze for a moment longer, eyes slightly narrowed and still clinging definitively to that last shred of defiance, and then abruptly she gives in as well and smirks back.

It's her turn now, so she suggests, "Dinner?"

It's getting late, after all. They've solved the case now, and the paperwork will still be waiting for them on Monday morning.

"Excellent idea," he grins. "I'm starving!"

It's that easy.

It hasn't always been, but they've learned a few things over the years, not the least of which when to draw a line under a situation. It's over and done with; they have their result and it's time to move on.

They take ten minutes to finish a handful of small tasks that really can't wait, and then they sweep out of the dungeon together, the stress of the day fading with every step they take towards the chilly November air.

Their younger colleagues watch them leave and heave a collective sigh of relief as the doors swing shut. Some days there really is no fathoming the pair of them.

He drives, for there are some things about which they don't relentlessly bicker, and it's a comfortable, quiet peace that settles between them. It lasts throughout their meal, no doubt aided by the tranquil and very cozy atmosphere of the tiny restaurant they have been frequenting for years. They found it quite by accident, and it has suited them ever since. Slightly peculiar, not too far from work or their homes, and tucked well out of the way of any and all tourists. It's perfect.

They laze over the meal, relaxing in each other's company and letting the week fall away from them. They laugh and they tease with easy familiarity; hints of that old, effortless flirtation rising naturally and warmly between them as the evening wears on.

It's very cold when they finally make a move and step back outside. Their breath fogs in the icy, still air. The crisp scent of a coming frost is apparent to both of them, as is the trace of something else. Boyd inhales deeply, identifying the unmistakable scent of a bonfire.

"It's the fifth," he says suddenly.

"It has been all day," she needles.

He ignores her. "I had completely forgotten," he continues, glancing around. She gives him a wicked grin.

"Remember, remember the fifth of November…" she intones slyly and he turns, giving her an impeccably disdainful glare.

She smirks. Gleefully.

"Come on," he urges, taking her gloved hand in his and leading her in the opposite direction of his car. For once she doesn't question, instead she just walks beside him. Truthfully, she doesn't want the evening to end just yet, and she's more than a little preoccupied with the feel of his hand firmly holding on to hers. If only they weren't wearing gloves…

They don't walk for long, and in fairly short order they emerge from the tangle of side streets into a lesser park. There are hundreds of people gathered, watching as the enormous bonfire consumes a straw Guy Fawkes in the center of the wide open space. Boyd leads her up a slight incline, away from the mass gathering and they stop near a rather forlorn and leafless tree, turning to view the scene sprawled out before them.

Bright orange flames roar impatiently over carefully stacked and piled wood, licking hungrily over the quickly perishing effigy of the long-ago traitor until a fierce blaze of white heat consumes him entirely and the crowd roars its approval. As the sound dies away the crackling and popping of the raging fire fills the cold night air.

Sparks glitter like flashes of molten bronze in the darkness as they leap high above the tendrils of burning orange; they are caught in the breeze and swirl around one another - a mini-show before the real spectacle begins.

The darkness wraps comfortably around them as the scent of wood smoke drifts pleasantly on the wind and despite her thick coat and her gloves, Grace shivers as the slow chill seeps through the layers of her clothing.

With the fire slowly dying down, music sounds from hidden speakers and as the first rocket whistles its way cheerfully up into the sky before exploding loudly and forcefully in a brilliant shower of falling colour, Boyd steps quietly behind her and gently pulls her back against his chest, his arms winding securely around her. Holding her, grounding her, warming her.

Grace leans back into him without conscious thought, utterly transfixed by the show.

It's loud, it's explosive and it's beautiful. Momentarily intense and all-consuming.

Until she feels Boyd rest his head next to hers and her attention is abruptly diverted. His arms tighten around her, holding her closer still and she wraps her own arms over them, gloved fingers sliding between his.

Caught as she is by the mix of him and everything else - his warmth and the crisp, cold air; the blending scents of him, smoke and the slight, arid trace of gunpowder; the whistle, crackle and boom of the fireworks; the thrilling sensation of the length of their bodies pressed together and the spectacular scene before them - there's no chance for her to analyse. No time to think. And suddenly his lips have found their way past her scarf and are gently pressed against her skin, trailing delicately along her neck.

Everything else just fades away as she turns to look up at him. His eyes are intense as he stares down at her, and she can see so many things there. Everything they've always avoided, everything they've always put off. Everything they've always wanted.

Tonight is one of those nights.

On the surface there's nothing particularly remarkable about it - the spectacular light show aside. Seemingly it's just an ordinary evening, like so many others in a long, unending succession. Except tonight is the kind of night where a single tiny spark is all the catalyst needed to turn the world on its axis. To take their carefully balanced, structured existence and completely upend it. To change everything; irrevocably and eternally.

And there are plenty of sparks in the sky.

The tension arcs and flashes between them, and when their lips meet in that first brush of spine tingling, electrifying contact, they know.

It's a tiny moment, but in it they can see it all; everything that has led them to this moment, and everything they will share from this moment on.

Lacy strands of golden dust are raining down above them as the display comes to an end; the velvet darkness of the sky shimmers with a riotous final explosion of colour as the music reaches its crescendo and flames of the bonfire devour the very last of the logs and splintered planks before fading away into embers.

They don't notice. They are far too caught up in their moment.

They only needed that one, single spark.