Mens Suits, Marylebone Fire Station, London<br/>Seizure, 157 Harper Road, London

A new Artangel project takes visitors into a spooky world in miniature, while a second installation is shortlisted for the Turner Prize

(Marcus Leith)

There's something about scaled-down versions of everyday objects that really disturbs me. The mere sight of a doll's house sends shivers down my spine, and I can hardly bear to think about poor Gulliver waking up to find the world in miniature. The reason for this fear, I suppose, has something to do with the uncanny, that theory which says we are unsettled by things that are not quite as they should be.

Uncanny is certainly the word for Charles LeDray's Mens Suits, a new installation by the American artist for the commissioning agency Artangel. The setting is a disused Victorian fire station in Marylebone, central London, and as soon as you walk in you feel like you've been thrown into the action of some creepy fairytale.

Outside, the building is all red brick and gothic finials. Inside, the empty garage remains intact, complete with a firemen's pole for whooshing down in emergencies. So far, so spooky. But just to unnerve you a little more, three displays of clothes are arranged in the centre of the room. Why are they there? More disturbingly, why do the jackets, shirts, ties and trousers – clearly the wardrobe of an adult male – look like they were made for a man the size of a two-year-old?

It's hard not to be curious. You look closer, hoping to find clues about the owner. In the first display there are more than a hundred ties arranged around a table, all neat except in one place where they have been messed up. Somebody seems to be angry. Next to the table a miniature tailor's dummy is dressed immaculately in a shirt, jacket and tie. In each vignette a ceiling panel hangs over the clothes at what would be normal height for the man who inhabits this world. You have to bend down to get a proper view.

Across the room three circular rails are hung with miniature jackets and shirts, all clean and ironed. On a table there is a pile of carefully folded T-shirts. The style of the clothes is distinctly 1950s, with boxy jackets and short-sleeved shirts covered in abstract Cold War designs. It could be the shrunken wardrobe of a young JFK.

In the third display the clothes tumble out of scaled-down laundry bags. There is an ironing board and a Lilliputian ladder. A sense of absence fills the space. Whoever was here may have left quickly, with no time to tidy up. Where has the owner gone and when will he be coming back?

Outside, I'm back in the normal world. But Mens Suits has done its work and I half expect to see a doll-sized man coming towards me.

It's this power to challenge your view of things that links all Artangel's projects. But in the best of them – most memorably Rachel Whiteread's House – the settings and work have been inextricably linked. As a result you look for a connection between the fire station and clothes in Mens Suits which, disappointingly, seems to be absent.

There's no such problem with the other Artangel project currently running in the capital. This is Roger Hiorns's Seizure, an installation in a former council flat in Elephant & Castle, which has won the young British artist a place on this year's Turner Prize shortlist.

Last summer Hiorns waterproofed the flat, filled it from the floor above with 75,000 litres of warm copper sulphate solution and left it for several weeks. When the solution was drained, the action of the chemicals left the ceilings and walls covered in glittering blue crystals. The installation proved so popular that it has now been reopened for a second run.

Visitors are invited to enter Seizure through the flat next door. Inside, it is dark, decaying, ordinary. Then you step through a hole in the wall into an amazing blue grotto ... It's an extraordinary feeling to experience the mismatch between the outside of the building and the inside. The shards of crystal that cover every surface twinkle under bare lightbulbs, their colour deep and intense.

Hiorns has criticised the Modern Movement in architecture for its vision of mega-blocks of identical flats for hundreds of families. For him, this collectivist ideal denies the differences between the people who live in them. What Seizure does is grab back one of these homes at the end of its life and transform it into an audacious expression of the individual. You come out dazzled, feeling that magic might be everywhere, even behind the windows of a boarded-up flat.

'Mens Suits' to 20 September; 'Seizure', to 18 October (Artangel: 020-7713 1400)

Charles Darwent is away