You know what? Maybe the fundamentalists are right. Break a rule just once and you open the proverbial flood-gates. The thin edge of the wedge, the slippery slope, beckons you. Mark Twain observed that once a man begins to commit murders, then soon he will find himself thinking little of theft, and may eventually end up taking the Lord's name in vain. Such is the power of habituation to dull our sensibilities. A couple of weeks ago I broke a long-standing rule of mine and visited a restaurant that had only recently opened. Now, a few weeks later, I've done it again. It's generally not a good idea to do this. Restaurants are like any other enterprise, you design everything as best you can, but the finest planning often doesn't foresee all the possibilities that can occur when the sub-systems start to inter-react - or to put it simply, new restaurants need time to settle in.

This week I was off to dinner with Mary Finnegan and we met in Dalkey. I'd asked her a few days earlier if she'd heard of anywhere good, and it happened she had. A restaurant on Dun Laoghaire harbour was her suggestion, a place called Purple Ocean, so she booked it for us. As we drove along the seafront in Sandycove, a wall of purple lights was visible in the area of the harbour, about a mile away. 'Could that be it?' I asked. 'That's definitely it', said Mary. At the roundabout in front of Restaurant na Mara we turned down toward the sea and parked outside the terminal building. A short walk took us to the entrance steps of Purple Ocean. I'll describe them, because they impressed me. They're steel and have an open tread, they slope gently upwards for a long way and they're underlit - in purple of course. At the end of the stairs you find a two-storey building lit prettily with outdoor downlighters, also purple.

Inside it's very new and shiny. The interior lighting has a, well, purple hue; the tables are black marble, the chairs upholstered in blue. I should point out that if the blue end of the spectrum isn't to your liking, this restaurant may not be the place for you. The tables are very prettily set - even the nightlights sit in a cradle of (blue) amethyst crystals and the napkins are, okay I'll say it, blue. The very first thing that I noticed - other than the colour of the lighting - was that Purple Ocean doesn't suffer from a lack of staff. It scores where many newly opened restaurants fail, it has enough staff to cope, even in the event of a customer invasion. And it wasn't just numbers, they were all very professional and the service throughout the evening was impeccable.

Both the menu and the wine list come in very smart covers of brushed aluminium, which nicely harmonise with all the good design in the room. The wine list runs to a few pages, and although there are some wines around the €20, many cluster around the €30, which makes any thought of a second bottle disappear. Mary decided she wanted a red wine for a change, so I chose a Salice Salentino - one I like from Candido. The wine list doesn't just list the wines, it also has some effusive descriptions of each wine in a high rococo style, some of which are real jewels.

Good breads came to the table with a bottle of mineral water for me, while we studied the menu. Lots of likely candidates to choose from, but in the end Mary began with crab cakes and I picked the devils on horseback. These arrived on beautiful plain white crockery, Mary's like an oblong dish, and mine like a long, slim fish platter which only just fitted onto the table. The crab cakes were in a fine crumb and they had a very light texture, although not strongly crab flavoured. My devils on horseback were superb; chicken livers wrapped in bacon and cooked to perfection, leaving the livers totally melt-in-the-mouth. Definitely one of the best dishes I've eaten of late.

For her main course Mary chose the slow-cooked lamb shank and I had the tuna steak. Looking at these two beautifully presented plates another thought came to mind. You shouldn't come to this restaurant if you're not hungry. Mary's lamb shank was big, as well being succulent and cooked to the point where it fell off the bone. My tuna steak was about the size of an old 45 record and about a half inch thick. With these came another pretty plate of our vegetables; some really tasty potatoes gratin, some carrots Julienne and broccoli. Once again, these dishes were expertly made, good to eat and both of them cost less than €20.

Apart from the good food and excellent service, Purple Ocean has another major plus. It has very fine views. One side of the restaurant is plate glass, and through it you see the sails and rigging of the yachts that bob gently in the marina. If there was a decent day, there are outdoor tables along this side, of the extruded aluminium type that you find on French boulevard cafes, which is worth knowing as Purple Ocean is open from 10 in the morning for brunch or early lunch. While we're on the subject of views, there's an upstairs as well, seating about a dozen people, which has to be the southside's answer to the Gravity Bar. 360 degrees of glass means that you have views over all of Dublin Bay, the whole sweep right around to Howth. If I had a foreign visitor I'd take them right here, I don't know of a better vantage point.

We finished the meal with an espresso, and a good one too. A bill for €82.90 not including service was remarkably good value for this fine meal in very smart surroundings.