By MARK ALAN LOVEWELL

The surprise 60th wedding anniversary party for Louis S. and Mary Larsen on Sunday at the Chilmark Community Center will go down in history as one of the town’s great capers.

The ability of 200 people to keep the secret from Chilmark’s notoriously in-the-know couple was remarkable.

The afternoon party drew visitors from all the Island towns and from afar. When Mary and Louis Larsen joined their daughter Kristina for a ride across the street to the community center, they thought they were going to a Jack and Jill baby shower.

Even when they crossed the threshold into the center and were greeted by all their friends, it took a while for the message to sink in: this was not a baby shower. It was the best surprise party an Up-Island family had pulled off in a while. The scope and scale of organizing reached out across the Atlantic.

Even a day after the party, the couple was seated at their kitchen table looking at the pile of greeting cards, trying to understand how their four children had pulled this off, using months of planning without prompting their knowledge or suspicion.

Mary Larsen has a well-deserved reputation for knowing a lot about the goings on in Chilmark. From 1948 to 1995 she worked in the Chilmark town hall. From 1972 to 1995 she was the selectmen’s executive secretary — and often knew more about the affairs of the town than the board she served.

Louis Larsen, 82, spent a career on the Atlantic Ocean knowing where the schools of fish were, from the Grand Banks down to the Bay of Campeche. Since retiring, the captain has turned his area of interest ashore and to the affairs of his four children, their fish markets, and their children. Mr. Larsen has always had osprey eyesight when it came to knowing where the fish were, the fishermen, and the whereabouts of his grandchildren.

To Betsy Larsen and her brother Louis Larsen, being able to pull off a surprise was a bigger deal than pulling off a big party with a lot of food. The two siblings, plus their eldest brother, Dan, all now own fish markets. Good meals are part of the family tradition. Surprise parties are tough.

Well before the anniversary couple arrived at 1:30 p.m., the Chilmark Community Center was a party scene and beverages were being served. A huge banner with the outline of a pink heart hand-drawn with the names Louis and Mary inside was hung on the wall. Buffet tables were covered with seafood, sandwiches and snacks. Roy Scheffer opened fresh oysters he’d pulled from Katama Bay. The chocolate dessert table was extraordinary.

A tree stood on the community center stage as a centerpiece. Each branch was decorated with paper leaves. A colorful leaf held the name of each one of the 10 grandchildren and five of the great-grandchildren.

Natalie Larsen, two months old, from West Tisbury, was the youngest great-grandchild. Her proud parents Dan and Shannon Larsen paraded her around and introduced her to extended family and friends.

Photographs of the honored couple were matted and framed and displayed on every table. The pictures had been snuck out of the Larsen family homestead while the couple was away on holiday months ago and duplicated. Louis Larsen, the son, said his sister Betsy commandeered the photographs and had them digitally copied. She safely returned the originals to the house, well before the parents had returned.

The honored couple spent a good deal of the party in disbelief. Louis Larsen walked around with a half-eaten lobster roll for most of the time, saying hello to his friends and often shaking his head.

His childhood friends Jimmy Morgan of Chilmark and Hershel West, now of Oak Bluffs, shared in the fellowship of working to pull a fast one on their waterfront pal. Mr. West said he truly enjoyed the fun.

Mr. Larsen said later that he spent more time at the party startled by the surprise, than by the event’s purpose, a celebration of an anniversary.

For days Edgartown Seafood, the Edgartown fish market owned by Daniel Larsen, had a sign out in the window saying “closed Sunday.” When Louis Larsen asked a grandson why the market was going to close on a Sunday, he got an acceptable explanation but it wasn’t about any party.

Come Sunday, the memories came rushing forward easily.

Louis Larsen of Chilmark and Mary Smith of Edgartown met for the first time at what today is the Art Cliff Diner in Vineyard Haven. Each had come from a different end of the Island to go bowling next door. When it came to evening youth events, bowling was popular at the time. The two were 21 years old.

They got married in Edgartown on April 24, 1948.

A copy of the wedding announcement that appeared in the Vineyard Gazette was nicely framed near a set of flowers and a nicely decorated wedding cake.

Nelson Smith, 83, and his brother, Mike, of Edgartown, gave their sister special greetings. The Larsens and their progeny filled the place. Grandson Aaron Larsen and his wife, Fiona, came all the way from Belfast, Ireland, for the event. Just about all of the grandchildren were there. Then there were friends of all Island professions, doctors, lawyers, politicians, farmers and fishermen.

Stanley Larsen, owner of Menemsha Fish Market, showed up wearing a tie, and so did a couple of local fishermen.

Even Captain Mike deConinck, who fishes out of Fairhaven, had come up from Florida just to share in the moment.