It turned out to be a hoard of photographic treasure, for which the only custodians for many years had been pigeons, which had liberally done what pigeons do, all about.
Stacked in piles on the floor were thousands of glass plate negatives, the work of a largely forgotten Shrewsbury photographer, James Mallinson.
That discovery 40 years ago has proven a goldmine, as among other things Mallinson had been commissioned to record photographically some of the major developments in the county town in the early decades of the 20th century, such as the rebuilding of the English Bridge in the 1920s, and in the 1930s the clearance of many historic properties in the Barker Street area, the building of the Granada cinema, and the construction of Shelton water works.
And a team of volunteers at Shropshire Archives are involved in a continuing programme of detective work to identify as many of the photographs as they can and put them online.
"The quality is superb. He was a brilliant photographer," says Tony Price, who has been working on the photographs to identify and catalogue them.
His particular favourite is a view of the old English Bridge.
"I think that's magic. You are talking about the centre of Shrewsbury and there is a cow sauntering across the English Bridge and nobody is bothered."
While some of the pictures are straightforward to identify, others - particularly Mallinson's portrait work - are not, and Tony has been greatly aided in working out what is what through the salvage of Mallinson's documentary records, which has meant some can be identified by cross-referencing.
Tony Carr was the local studies librarian in Shrewsbury when he got a tip-off from one of the regulars at the library, Stan Turner, himself a keen amateur photographer, which led to the discovery of the photos.
"Stan Turner said: 'You may be interested, Mrs Mallinson has died. I think there may be photographs in the house,'" recalled Tony.
Widowed Lucy Marion Mallinson, of 13 Frankwell, died at the age of 86 on January 9, 1978, so the tip must have been soon after that.
"I contacted the executor, who was a solicitor on Claremont Bank, I think, and said: 'I understand there may be some photographs in the house, we would be interested in having them. Would that be okay?' He said: 'Sure.' I think he gave us the key."
Tony Carr went to the house with the library van driver - he thinks it was Malcolm Brown, but wouldn't swear to that.
"It was a bit spooky," he said.
The property had the air of a place in which not much had been done for decades.
Downstairs was a commercial room, and upstairs was living accommodation which they did not look at.
"The attic was approached up a staircase which was built into what had been the party wall of a house that had been demolished to make the Wheatsheaf car park. Because that whole wall had never been sealed properly when they demolished the house on the car park side, the whole thing was soaking wet. You could poke your finger into the plaster and water came out. It meant that the treads up to the attic were rotten in places.
"We had to be very careful going up, working out which step you could tread on."
They gingerly made their way to the attic, which had a window in which a pane of glass was broken.
"The place had been lived in by pigeons. And there, on the floor, were stacks of whole plate glass negatives, stacked this high (indicates about a foot) with no covering.
"A whole plate negative is about that sort of size (indicates about 10ins by 8ins). They're beautiful photographs because the image is crystal clear. The clarity is first class. There were lots of piles."
Although Tony will have come across the name of Mallinson through some of his photographs already in the local studies library's collection, he says he did not know what to expect.
"I thought gosh, this will be worth investigating. There were about 3,000 of them. The vast majority were whole plate. Some of them were cracked. All of the piles had suffered from the attention of pigeons and the damp so that the emulsion side of the negative in some cases had become rather sticky at the edges where the atmosphere had got to them.
"Also up there were his business records, day books and suchlike which I thought would be useful possibly to identify some of the photographs in due course. Then we had to work out how we were going to get them out."
The pair carefully carried the precious negatives down the stairs and loaded them into the van, which took half a morning, and they took them back to St Mary's Hall, where the local studies library was based at that time.
Here Tony Carr had the opportunity to prise the negatives apart and have a good look at them.
"Amazingly they came apart quite easily and dried out individually. Some of them needed cleaning up, particularly where the pigeons had roosted.
"They're interesting from the point of view of a cross section of work of a photographer in the 1930s. It's a bit of luck they had been retained in the studio and not just tipped."
Tony Price, who is 73 and from Cosford, has been a volunteer at Shropshire Archives for five or six years, and is part of the team cataloguing photographs to put them online, which is how he came across Mallinson's collection.
In working out those which are a puzzle, he draws on the local knowledge of himself and other volunteers, research, and clues such as Mallinson's records.
"We all put our tuppence worth in," he said.
"Some of them are obvious, you just look at them and know it's the English Bridge or Welsh Bridge or whatever, and we have got somebody in the archive who knows Shrewsbury intimately and she will say 'that's Grope Lane' or whatever.
"There are though photographs we put as unidentified, as we don't know who or what they are.
"There's a superb picture of a vicar, his wife, and two daughters. It's magic and beautifully posed. But there's not a clue of who he is."
Nevertheless he finds the detective task is fun.
"I really enjoy coming here. I really look forward to Thursdays."
Many of Mallinson's photos can be viewed online through Shropshire Archives' website www.shropshirearchives.org.uk, and out of the archives' entire photographic collection of over 45,000 images, over three quarters are viewable online.
As for Mallinson himself, Tony Price's researches have found that he was born in 1891 and his family came from Bradford.
James was educated at Shrewsbury Technical School, where he obtained a certificate in advanced technical drawing. In 1919 he married Lucy Kynaston from Wem.
A professional photographer, his studio was at 13 Frankwell. His work included commissions, brochures - including school brochures - and portraiture, not just in Shrewsbury but across the county. He was the go-to photographer for Arthur Ward, the borough surveyor of Shrewsbury, which gave him access to various major developments.
Mallinson died on May 23, 1959. If there were any obituaries or even death notices in the local press, we haven't found them.
So it may be that he was by that time a forgotten photographer who died without trace.
However, thanks to that 1970s discovery and the continuing work of Shropshire Archives, Mallinson's name lives on through his legacy of astonishing images and enduring record of the seismic changes in early 20th century Shrewsbury.
All pictures used with this feature are courtesy of Shropshire Archives and are from the Mallinson collection.