144 Drummond Street, London NW1 (020 7388 9962). Meal for two, with wine and service, £60-£150

There are lots of restaurants like Sushi of Shiori. It's just that none of them are in London. Or Britain. To be sure of finding another place like this you will have to head to Tokyo, where they cluster like so many pigeons around a split sack of seed. Here, restaurants with just one chef and seven seats are hardly common. But it really couldn't be simpler: an open kitchen where the young chef, a graduate of Mayfair's buttock-clenchingly expensive Umu, does his intense, detailed, obsessive-compulsive thing. There is a bar with three seats, so you can watch him doing it. Behind is a counter in the window with four seats looking out into Drummond Street, a road near Euston station famed only for its cheap Indian restaurants and colourful drunks.

So should you go? Yes, though not for its novelty. Those with a sweaty, overheated love of Japanese food will find a lot to get frisky about here. But there is a problem, and it is so glaring, so big, that it needs mentioning early. The problem is this: the rice. I have heard certain sushi heads claim that the good stuff is "all about the rice". This has always seemed a rather silly, pompous thing to say. How can it be about the rice, when the thing that goes on top of it costs so much more?

And then I tried Shiori's nigiri sushi – the thumb-length pillows of rice with raw fish on top – and I realised it really could be all about the rice. Good sushi rice should be just warm, each grain capable of letting go of the next with barely a shrug. Unfortunately the rice at Shiori just ain't all that: cold, claggy, under-flavoured, underwhelming.

It is such a shame, because everything else is so good. Although there is a longish menu of various sushis and sashimis, you can, when you book, ask for an omakase – a Japanese-style tasting menu prepared according to what's best and available. You name the price you want to pay per head, from £30 or so upwards, and a delicate Japanese woman with small feet and perfect hands brings it to you. We asked for an omakase for two for £45. It started magnificently, with four cylinders of white crabmeat, tightly wrapped in nori – toasted seaweed – with a fine dashi broth.

That was followed by slices of sea bass sashimi, arranged as an albino peacock fan tail, each carrying a dot of sticky plum sauce, and on the side a small bowl of ponzu (citrus sauce), which we were invited to pour over. In that combination of the subtle and the sharp, the clean and the precise, it was exactly what lovers of Japanese food get most excited about.

There was another bowl of cool dashi broth with, lying at the bottom, thin, slippery soba noodles. Most impressive of all was the sashimi, arranged with exquisite attention to detail: on one side, a hollowed-out lemon, its cut edge serrated, the peel bowl filled with chopped mackerel and tuna. On the other side, slices of sweet scallop brushed with a slick of something that lifted the flavour without declaring itself. We failed to identify it and had to ask: it was truffle oil. Too often merely tiresome, here, used with a light hand, it was perfect. In between there were slices of the best raw fish, deftly sliced.

And then the disappointment of the sushi. It looked beautiful and the fish itself really was marvellous. The attention to detail – the way slices of spring onion were balanced here, or shining balls of bright-orange salmon roe were clustered there – beggared belief. The eel was especially good. But the rice both here, and on a subsequent course of sliced wagyu beef, seared and presented nigiri style, made us mourn self-consciously. There were compensations: a superb black sesame ice cream, the slate-grey shade of an expensive kitchen floor, and an equally pleasing plum wine sorbet. We despatched a very good bottle of sake from a carefully built list, and hugged ourselves at our cleverness for even being here in the first place. There really is nothing like this in London. And in places it is shimmering with brilliance. The rest, you know.

This week Jay has also been...

sharing plates of Nando's chicken with his son, who has been recovering from an operation in hospital. The ward dietician had no objections.

Side order: a feast for the eyes

According to research by Bristol University's Jeff Brunstrom, and presented to the snappily titled Society for the Study of Ingestive Behaviour in Pittsburgh, looking at pictures of food before you eat may influence how satisfied you feel afterwards. Show someone an image of a pile of fruit, and then give them a smoothie made with half the amount, and they will declare themselves fuller than someone shown a picture of the correct amount. Having been told this, of course, it almost certainly won't work on you, but at least you now know…


Email Jay at jay.rayner@observer.co.uk or visit theguardian.com/profile/jayrayner for all his reviews in one place