In the summer of 1958, a Shetland teenager asked if he could take part in the excavation of an ancient church on St Ninian’s Isle, a tiny island linked to the Shetland mainland by a sand bar. Just a few hours later, he uncovered a cache of silver brooches, bowls and other artefacts that became known as the St Ninian’s Isle Treasure.

Now the treasure, which is normally kept in Edinburgh at the National Museum of Scotland, has returned to Shetland for the 50th anniversary of its discovery.

The treasure of some 30 items dates from around 700ad. As well as the brooches and bowls, a spoon and a number of swords broken into pieces, it includes some objects that still have the experts guessing. Ian Tait, the museum’s curator of collections says: “There is an artefact that could be a scribe’s tool - possibly used to crease parchment - but the most intriguing are three silver conical pieces, shaped like salt shakers, that we are still puzzling over.”

A foot-long bone from a marine mammal, possibly part of a porpoise’s jaw, was also found among the silver, leading experts to believe it had some religious significance.

“That the swords were broken into pieces points to the treasure having been hidden because of the value of the silver, and may have been the property of a group of wealthy people who were protecting it from Viking raiders,” says Mr Tait.

And the fact that the treasure was still in its hiding place some 1,200 years later points to its owners either having fled the area forever or having been killed, captured or enslaved by the Vikings.

The treasure will be on show at the Shetland Museum and Archives until October 5. School tours will be available.

T 01595 695057.