Macrosant is housed in a massive block on Kingsway, with big steps and a steel globe sculpture and plate-glass windows. From the Costa Coffee across the road, I have a pretty good view of it.

“Anything doglike,” I’m instructing Sadie, behind an open copy of the Evening Standard. “The sound of barking, baskets under desks, dog toys…” I take a sip of cappuccino. “I’ll stay here. And thanks!”

The building’s so massive, I could be waiting here awhile. I flick through my Evening Standard and slowly nibble my way through a chocolate brownie, and I’ve just ordered a fresh cappuccino when Sadie materializes in front of me. Her cheeks are flushed and her eyes are shining and she’s glowing all over. I pull out my mobile phone, smile at the girl at the next table, and pretend to dial a number.

“So?” I say into the phone. “Did you find a dog?”

“Oh, that,” Sadie says, as though she’d forgotten all about it. “Yes, there’s a dog, but guess what-”

“Where?” I cut her off in excitement. “Where’s the dog?”

“Up there.” She gestures. “In a basket under a desk. It’s the dearest little Pekingese-”

“Can you get a name? An office number? Anything like that? Thank you!”

She vanishes and I sip my new cappuccino, hugging myself. Shireen was right all along! Jean lied to me! Wait until I get on the phone with her. Just wait. I’m going to demand a full apology and full office rights for Flash and maybe a new dog basket as a goodwill gesture…

I glance through the window and suddenly spot Sadie drifting along the pavement, back toward the coffee shop. I feel a tiny spike of frustration. She doesn’t seem in any hurry at all. Doesn’t she realize how important this is?

I’m ready with my mobile out as soon as she enters. “Everything OK?” I demand. “Did you find the dog again?”

“Oh,” she says vaguely. “Yes, the dog. It’s on floor fourteen, room 1416, and its owner is Jane Frenshew. I’ve just met the most delicious man.” She hugs herself.

“What do you mean, you’ve met a man?” I’m scribbling it all quickly on a piece of paper. “You can’t meet a man. You’re dead. Unless-” I look up with a sudden thrill. “Ooh. Have you met another ghost?”

“He’s not a ghost.” She shakes her head impatiently. “But he’s divine. He was talking in one of the rooms I walked through. Just like Rudolph Valentino.”

“Who?” I say blankly.

“The film star, of course! Tall and dark and dashing. Instant sizzle.”

“Sounds lovely,” I say absently.

“And he’s just the right height,” Sadie continues, swinging her legs on a bar stool. “I measured myself against him. My head would rest on his shoulder perfectly if we went dancing together.”

“Great.” I finish writing, grab my bag, and stand up. “OK. I need to get back to the office and sort this out.”

I head out of the door and start hurrying toward the tube, but to my surprise Sadie blocks my way.

“I want him.”

“I’m sorry?” I peer at her, flicking my mobile open out of habit.

“The man I just met. I felt it, right here. The sizzle.” She presses her concave stomach. “I want to dance with him.”

Is she joking?

“Well, that would be nice,” I say at last, in placatory tones. “But I’ve really got to get to the office-”

As I move forward, Sadie thrusts a bare arm across my path and I stop, taken aback.

“Do you know how long it’s been since I’ve danced?” she says with sudden passion. “Do you know how long it’s been since I’ve… shaken my booty? All those years, trapped in an old woman’s body. In a place with no music, with no life…”

I feel a rub of guilt inside as I remember the picture of Sadie, ancient and wrinkled in her pink shawl.

“OK,” I say quickly. “Fair enough. So, let’s dance at home. We’ll put on some music, dim the lights, have a little party-”

“I don’t want to dance at home to the wireless!” she says scornfully. “I want to go out with a man and enjoy myself!”

“You want to go on a date,” I say disbelievingly, and her eyes light up.

“Yes! Exactly! A date with a man. With him.” She points at the building.

What exactly is it about being a ghost that she doesn’t understand?

“Sadie, you’re dead.”

“I know!” she says in irritation. “You don’t have to keep reminding me!”

“So you can’t go on a date. Sorry. That’s the way it is.” I shrug and start walking on again. Two seconds later, Sadie lands in front of me once more, her jaw set.

“Ask him for me.”

“What?”

“I can’t do it on my own.” Her voice is fast and determined. “I need a go-between. If you go out with him on a date, I can go out with him on a date. If you dance with him, I can dance with him too.”

She’s serious. I almost want to burst out laughing.

“You want me to go on a date for you,” I say, to clarify. “With some random guy I don’t know. So you can have a dance.”

“I just want one last little burst of fun with a handsome man while I still have the chance.” Sadie’s head falls forward and her mouth pouts into the sad little O shape again. “One more whirl around a dance floor. That’s all I ask before I disappear from this world.” Her voice descends to a low, pitiful whisper. “It’s my last desire. My final wish.”

“It’s not your final wish!” I say, a bit indignantly. “You’ve already had your final wish! It was searching for your necklace, remember?”

For an instant Sadie looks caught out.

“This is my other final wish,” she says at last.

“Look, Sadie.” I try to sound reasonable. “I can’t just ask a stranger on a date. You’ll have to do without this one. Sorry.”

Sadie is surveying me with such a silent, quivering, wounded expression that I wonder if I somehow stepped on her foot.

“You’re really saying no,” she says at last, her voice cracking as though with emotion. “You’re really refusing me. One last innocent wish. One tiny request.”

“Look-”

“I was in that nursing home for years. Never any visitors. Never any laughter. Never any life. Just oldness… and loneliness… and misery…”

Oh God. She can’t do this to me. It’s not fair.

“Every Christmas, all alone, never a visitor… never a present…”

“It wasn’t my fault,” I say feebly, but Sadie ignores me.

“And now I see the chance of a sliver of happiness. A morsel of pleasure. Yet my own callous, selfish great-niece-”

“OK!” I stop in my tracks and rub my forehead. “OK! Whatever! Fine! I’ll do it.”

Everyone in my life thinks I’m a lunatic anyway. Asking a stranger on a date will make no difference; in fact, my dad will probably be delighted.

“You’re an angel!” Sadie’s mood has instantly flipped to giddy excitement. She whirls around on the pavement, the panels on her dress flying out. “I’ll show you where he is! Come on!”

I follow her toward the massive steps and push my way into the huge double-height foyer. If I’m going to do this, I need to do it very quickly, before I change my mind.

“So where is he?” I look around the echoing marble chamber.

“In a room upstairs! Come on!” She’s like a puppy straining the leash.

“I can’t just walk into an office building!” I hiss back, gesturing at the electronic security barriers. “I need a plan. I need an excuse. I need … aha.”

In the corner is a stand with the sign Global Strategy Seminar. A pair of bored-looking girls are sitting behind a table of name badges. They’ll do.

“Hi.” I approach briskly. “Sorry I’m late.”

“No problem. They’ve only just started.” One of the girls sits up and reaches for her list, while the other stares resolutely at the ceiling. “And you are…”

“Sarah Connoy,” I say, grabbing a name badge at random. “Thanks. I’d better get going.”

I hurry to the security barriers, flash my name badge at the guard, and hurry through into a wide corridor with expensive-looking artwork on the walls. I have no idea where I am. The building holds about twenty different companies, and the only one I’ve ever visited is Macrosant, which is on floors 11-17. “Where’s this guy, then?” I murmur to Sadie out of the side of my mouth.