Less than an hour later, they emerged in the early March sunshine and sat down on a bench to wait. A young slim blonde woman wearing blue trousers emerging from a large grey-blue coat strolled casually towards them. In Kate's pocket, her hand-held scanner vibrated and she got up to meet the newcomer: "Doctor – thank you for coming"

"Pleasure – what can I do for you, Kate?"

The three women shook hands and sat back down while Kate explained the situation. The Doctor retreated into herself for a moment and then exclaimed: "Heavens! She's at it again – slight change of target, apparently, but…"

Kate looked at the Doctor hopefully: "You know who She is, then?"

"Yes …I met her …some time ago – won't tell you when, it makes me feel old. But I should be able to get in touch with Her for you – Viviane and I got on pretty well then."

Osgood interrupted: "Viviane? You mean, like in "Merlin and Viviane"? That Viviane?"

Kate sighed: "So now they want us to hunt down fairies! As if aliens weren't enough."

The Doctor went on: "Yes, Viviane – the Lady of the Lake – she used auras before, you know, with Merlin and that crowd. I didn't think she was into killing people, though!"

"Can you take us to her?"

The Doctor frowned: "There may be a slight problem with that – I seem to have misplaced my Tardis…" Then she brightened up: "Doesn't matter – I'm going to summon Her instead; I just need water – now, where can I find water?"

Kate gestured towards the Thames behind them.

"Oh no, dear – not that kind of water – I need something quieter – like, a lake, or … I know, come on!"

And she ran towards the kerb to hail a cab. Kate and Osgood followed her, Osgood murmuring "I like her – a bit different, but she seems to have her head screwed on…" Kate nodded and added: "I hope you've got cash on you, because I don't, and I don't think the cabbie is going to be very happy if we tell him we can't pay him because we left in a hurry to meet a fairy."

"Don't worry, Ma'am – I always have £20 on me in case …well, in case – and if this isn't enough, we can always wipe out his memory."

The cab took them to Regent's Park and the Doctor guided them to a secluded area where a small pond nestled in a grove of willows. Osgood nudged Kate and whispered: "Don't you think we should check in with Josh and the Colonel? Maybe we should have brought back-up." Kate laughed: "I'm not afraid of fairies – besides, I've got my gun, just in case."

The Doctor had sat down on the grass and she beckoned to them: "I've summoned her – she's coming." A few minutes later, Kate's eyes were drawn to the middle of the pond. A beautiful woman was emerging from the water – or at least, she was probably beautiful – it was hard to know really, because Kate's first impression of her was a myriad of colours and deep blue eyes. She hardly heard the Doctor's parting words: "Hello, Viviane – long time no see. I'll leave you to it then – be safe, Kate, and I'll see you soon." As she left, she motioned to Osgood to leave Kate alone. Osgood, who saw only Kate standing near the pond, nevertheless took the hint, murmured: "I won't be far, Ma'am", and walked away.

Kate and Viviane were left facing each other. Now that Viviane was out of the water, Kate saw her more clearly – she had before her a slim woman with dark hair running down her back ,milky-pale skin, and piercing blue eyes – who appeared to be surrounded by a red mist. Viviane spoke first: "My friend tells me you are in need of my help – how can I assist you in your quest?"

Kate shook her head, trying to dispel the red glow around her interlocutor, and answered rather brusquely, as she always did when she was nervous: "You can begin by telling me why you've enchanted all those women, and why you've told them to kill people."

Viviane looked at her appealingly: "Please, Kate – do not assume the worst of me. I never wanted to hurt anyone. I may have, in the past but …Please let me explain."

Kate nodded and Viviane went on: "Matters of the heart are complicated and often deception and heartache occur… My intention was never to kill, but to help those women, get them to see the true nature of people so that they would stop wandering in gloom and find the Right One. My spell transformed their emotions, their inner feelings into colours, and that was supposed to help their hearts lead. But somehow, in some of them, my spell went horribly wrong, and they took it upon themselves to slay the darkest human felons."

Kate was listened attentively, or at least trying to, because the red glow around Viviane had not dispelled, and it was most disturbing: "So you manipulated their brain signals, but you got the programming wrong…"

"I am not sure what you mean – I cast a spell, but unfortunately magic is not perfect alchemy and one cannot foretell the consequences." Viviane took a step towards Kate and looked straight into her eyes. Kate felt suddenly very warm, as if Viviane's body irradiated heat – warm and a strange tingly sensation invaded her… When Viviane leant towards her and stroked her face, she stiffened and took a step back, but an irresistible pull drew her to Viviane again. And when Viviane's lips brushed hers, she did not resist anymore, and lost herself in the kiss.

Afterwards, Kate had no idea how long they had stayed together, entwined, at one with one another. She only knew that she had never felt so whole, so intense, so fulfilled. And when Viviane broke the embrace, Kate was engulfed by a sense of loneliness and loss she had never experienced so deeply either. Then Viviane spoke again: "You too have experienced heartache, Kate – but I see now that I have been wrong. The humans need to make their own mistakes to learn. Not all who wander are lost. I regret that I cannot give their lives back to those who have perished by my fault, but I will undo the spell. I wish you well, Kate – may you find your own path in love. Godspeed!"

As she watched Vivian's image getting dimmer and dimmer in the red glow, Kate murmured: "Thank you, Viviane – will I …will I see you again?" Silence answered. She remained a few minutes staring at the pond, motionless, before she shook herself and walked towards Osgood.

Osgood took one look at her boss and wished she had not left her alone. Kate was ashen, and her eyes burned strangely: "Are you all right, Ma'am? Do you need to sit down?"

"I'm fine, Osgood. We can go now – no need for us to catch a chill. And I need to phone the General. Let's catch a cab back."

"Yes, Ma'am." The sooner her boss was back at the Tower, the better, as far as Osgood was concerned – she'd never seen her look so flustered, almost feverish. It was a silent drive back, and only when they were safely inside the Tower did Osgood dare to inquire about what had happened at the pond.

Kate looked at her unseeingly for a minute, and then answered in a business-like tone: "I know fairy tales are not part of your everyday literary diet, Osgood, but you do know that what begins with "once upon a time" usually ends by "they lived happily ever after." I believe this will be the case…"