“It’s a maid.” She glares at me. “You should have grabbed it!”

“I’ll get it in a minute when she’s gone! Don’t stress! Just keep a lookout!”

I back right against the wall, praying that the maid or whoever she is doesn’t decide to come out on the terrace for a breath of fresh air and madly thinking of excuses if she does.

Suddenly my heart jumps as the French doors start moving-but they’re not opening. They close with a firm clunk. The next thing I hear is the click of a key being turned.

Oh no.

Oh no, oh no.

“She’s locked you out!” Sadie darts into the room, then out again. “Now she’s gone! You’re stuck! You’re stuck!”

I rattle the French doors, but they’re well and firmly locked.

“You idiot!” Sadie is beside herself with fury. “You absolute fool! Why didn’t you just grab it?”

“I was about to!” I retort defensively. “You should have gone to check if anyone was coming!”

“Well, what are we going to do?”

“I don’t know! I don’t know!”

There’s silence as we face each other, panting slightly.

“I need to put my shoes on,” I say at last. I head down the steps and slip on my wedges. Above, Sadie is still darting in and out of the room in frustration, as though she can’t bear to relinquish her necklace. At last she gives up and joins me on the grass. For a few moments neither of us meets the other’s eye.

“I’m sorry I wasn’t quicker at grabbing it,” I mumble at last.

“Well,” says Sadie, clearly making a supreme effort. “I suppose it wasn’t completely your fault.”

“Let’s go around the house. We may be able to slip in somewhere. Go inside and see if the coast is clear.”

As Sadie disappears, I creep cautiously over the grass and start moving along the wall of the house. I’m making slow progress, because every time I pass a window I duck down and crawl on my stomach. Although that won’t exactly help if one of the security guards comes along-

“There you are!” Sadie pops out of the wall beside me. “Guess what?”

“Jesus!” I clasp my chest. “What?”

“It’s your uncle! I’ve been watching him! He’s just been to his safe in his bedroom. He looked in it, but he couldn’t find what he wanted. Then he banged it shut and started shouting for Diamante. The girl. Odd name.” She wrinkles her nose.

“My cousin.” I nod. “Another of your great-nieces.”

“She was in the kitchen. He said he needed a private word and sent all the staff away. Then he demanded, had she been going in his safe and taking things? Then he said an old necklace was missing and did she know anything about it?”

“Oh my God.” I stare back at her. “Oh my God! What did she say?”

“She said no, but he didn’t believe her.”

“Maybe she’s lying.” My mind is working overtime. “Maybe that’s her bedroom, where the necklace was.”

“Exactly! So we have to get it now, before he realizes where it is and locks it away again. There’s no one around. All the staff have got out of the way. We can go through the house.”

I haven’t got time to think about whether this is a good idea or not. My heart pumping, I follow Sadie to a side door and in through a laundry room as big as my whole flat. She beckons me through a pair of swing doors, down a passage, then holds up a hand as we reach the hall, her eyes widening warily. I can hear Uncle Bill shouting, his voice increasing in volume.

“… private safe… personal security… how dare you… code was for emergencies only…”

“… not bloody fair! You never let me have anything!”

It’s Diamante’s voice, and it’s getting closer. On instinct, I dart behind a chair and sink down, my knees trembling. The next moment she strides into the hall, wearing a strange asymmetrical pink miniskirt and a teeny-tiny T-shirt.

“I’ll buy you a necklace.” Uncle Bill comes striding in after her. “That’s no problem. Tell me what you need, Damian will find it-”

“You always say that!” she shrieks at him. “You never listen! That necklace is perfect! I need it for my next Tutus and Pearls show! My whole new collection is based on butterflies and insects and stuff! I’m a creative, in case you hadn’t realized-”

“If you’re so creative, my love,” says Uncle Bill with a sarcastic edge, “why have I hired three designers to work on your dresses?”

For a moment I’m gobsmacked. Diamante uses other designers? The next minute I can’t believe I didn’t work that one out before.

“They’re… fucking … assistants!” she screams back. “It’s my vision! And I need that necklace-”

“You’re not using it, Diamante.” Uncle Bill’s voice is ominous. “And you’re never going in my safe again. You’re going to give it back to me right now-”

“No, I’m not! And you can tell Damian to fuck off, he’s a git.” She runs up the stairs, closely followed by Sadie.

Uncle Bill looks so furious, it’s as though he’s not quite in possession of his faculties. He’s breathing heavily and thrusting his hands through his hair as he gazes up the grand staircase. He looks so uncool and out of control, I almost want to giggle.

“Diamante!” he shouts. “You come back here!”

“Fuck off!” comes a distant cry.

“Diamante!” Uncle Bill starts to stride up the stairs himself. “That’s it. I won’t have this-”

“She’s got it!” Sadie’s voice is suddenly in my ear. “She’s taken it! We need to catch her! You go round the back. I’ll guard the front stairs.”

With scrambling legs I get to my feet, run back down the passage, through the laundry room, and out onto the lawn. I sprint breathlessly around the house, not caring if anyone sees me-and stop dead in dismay.

Shit.

Diamante is in a black, open-top Porsche, heading down the gravel at speed toward the front gates, which are hastily being opened by the security guard.

“Noooo!” I wail before I can stop myself.

As Diamante pauses to exit, she flicks a V-sign back at the house and the next minute is out on the street. In her other hand I can just see Sadie’s necklace, wrapped around her fingers, glinting in the sunshine.

There’s only one possibility: They’re not rhinestones, they’re diamonds. The necklace is studded with rare antique diamonds and worth millions of pounds. It’s got to be that. There’s no other reason I can think of that Uncle Bill would be so interested in it.

I’ve Googled all sorts of websites on diamonds and jewelry, and it’s amazing what people will pay for a 10.5-carat D-color diamond mined in 1920.

“How big was the biggest stone in the necklace?” I say yet again to Sadie. “About.”

Sadie sighs noisily. “Half an inch or so?”

“Was it very sparkly? Did it look flawless at all? That could affect its value.”

“You’re terribly interested in the value of my necklace all of a sudden.” Sadie gives me a resentful look. “I didn’t think you were so mercenary.”

“I’m not mercenary!” I say indignantly. “I’m just trying to work out why Uncle Bill was after it! He wouldn’t waste his time unless it was valuable.”

“What difference does it make if we can’t lay our hands on it?”

“We will lay our hands on it.”

I have a plan, and it’s a pretty good one. I’ve been using all my detective skills in the few days since we got back from Uncle Bill’s house. First of all, I found out about Diamante’s next Tutus and Pearls catwalk show. It’s this Thursday at the Sanderstead Hotel, 6:30 p.m., private guest list. The only trouble was, I couldn’t see Diamante putting me on the private guest list in a million years, bearing in mind I’m not a photographer from Hello! or one of her celebrity chums or have four hundred quid to spend on a dress. So then came my master stroke. I emailed Sarah in a friendly way and said I’d really like to support Diamante in her fashion venture and could I come and talk to Uncle Bill about it? Maybe I would just drop over to the house on spec, I suggested. Maybe tomorrow!!! And I added a few smiley faces for good measure.