He couldn't remember where he was, or what he was doing, the first time he saw her smile.

Oh, not that cheeky grin he saw in that pub on their very first case together - although that was adorable enough on its own, lighting up her face in a way that demanded he smile back. No, that wasn't the smile that stopped him dead in his tracks, set his heart racing, and stole the breath from his lungs.

It was their fourth case together - or maybe their fifth, he couldn't remember now - and he'd said something to make her laugh. They'd been getting on so well, bantering in a way he'd never been able to do with anyone before, and before he could help himself he let fly with a ribald innuendo that would have made his mother faint.

Barbara Havers, however, did not faint.

Oh, no. Not Barbara.

Instead she threw her head back and laughed, clear as bells, her eyes glowing vivid green, the sunlight striking off her red hair, and her smile quite simply radiant. He could do nothing but stop and stare as he forgot how to breathe, and he realised, quite suddenly, that his nosey, hardheaded, dowdy, frumpy partner was beautiful.

Christ, but she was stunning when she smiled like that! No cheeky grin or halfhearted grimace - it was the first full-blown smile he'd ever seen from her, and it was heartstopping.

In that moment, he almost wanted her. Not quite, but almost.

It couldn't last forever, of course. Within the hour they were back to bickering, the namecalling and insults flying fast and furious. She was scowling and red-faced, and he had never wanted to strangle anyone so much in his life. He heard her call him something particularly vile, and he couldn't help it; he burst out laughing.

She scowled even more fiercely for a minute, and then she lost the battle - she joined in, laughter pealing out, and smiled again, and he made a silent vow to make her smile like that just as often as he possibly could.

She smiled up at him just that way a decade later, wearing white with roses in her hair, as they danced their first dance as husband and wife, and though the laugh lines fanned out from her eyes and grey touched her fiery hair, that smile stopped his heart and stole his breath just as it always had.

Barbara Havers was many things: cranky, temperamental, bawdy, fiercely intelligent, passionate, devoted, hardheaded, compassionate. Most would call her passably attractive - even, on occasion, adorable. Few would call her pretty on the best of days, for few saw past the frumpy clothes and scowl that masked her true heart.

But he saw the truth of his partner, his Barbara, the first time she truly smiled, and through all that was to come, he never could quite forget how beautiful she could be, because when she smiled, he saw the heart of her, the kindness and the strength and the compassion.

And it made her beautiful.