Mystery surrounds the whereabouts of the historic first page of the Ulster Covenant signed by Sir Edward Carson at Belfast City Hall.
Preparations are underway to celebrate the centenary in September of the signing.
More than 470,000 men signed the oath. Women signed the the declaration, an accompanying promise of support.
However, the collection, held by the Public Records Office, does not include the page signed on camera by Carson.
Sir Edward put pen to paper on 28 September 1912, the first of ten unionist grandees to put their names to a pledge to resist what they called "the threatened calamity" of Home Rule for Ireland by "all means which may be found necessary".
The moment of defiance of the Westminster government was captured for posterity by both photographers and an early cinema cameraman.
The vast majority of those signatures are contained in dozens of boxes donated by the Ulster Unionist Council to the Northern Ireland Public Record Office in 1959.
However, the original page one of the covenant with its ten signatures appears to be missing.
Photographs exist of the page and there are also images of a souvenir parchment signed by Carson alone.
The Public Record Office told the BBC it has never held the first page signed by Sir Edward on a table which is now kept in the council chamber in Belfast City Hall.
It believes the Ulster Unionist Council held on to the front page and had it on display in their old offices in Glengall Street in central Belfast for many years.
However, the Ulster Unionists said they could not verify this.
The party no longer has an office in Glengall Street - it is currently based in east Belfast.
A UUP spokesman told me the party had deposited historic records with the Public Record Office in good faith, and was concerned and annoyed about the question mark over the whereabouts of the first page.
I met up with local historian Henry Bell in the Public Record Office reading room to get his take on the significance of the missing page.
The history and politics lecturer told me that it was no coincidence that "the number one signature on the very first sheet in the very first folder was by Edward Carson.
"They had focussed in on Carson as the symbol of unionism and Ulster's resistance, so his signature would be the moment to start the whole process and I find it absolutely amazing that we are not looking at his signature in front of us," Mr Bell said.
He said that "to look at the actual signature would be absolutely wonderful" and he would love to see it discovered and put on display in time for the centenary.
Perhaps someone has the document and doesn't realise its significance.
Or could it be taking pride of place on someone's wall, without the knowledge of either the Public Record Office or the modern day UUP?
With the calendar ticking down to the 100th anniversary in September, the hunt for the covenant's first page looks increasingly urgent.
Just like their forebears, unionists may have to employ "all means which may be found necessary" to turn up the missing heirloom.
If you know where it is let me know via Twitter @markdevenport .