1975 opened with an IRA cease-fire, which lasted for most of the year. It has always been known that British officials talked to representatives of the Republican Movement - but for 30 years controversy has surrounded exactly what was on the table.
Newly released State papers shed new light on what the British were up to - they wanted to offer just enough to keep the cease-fire going, in the hope that Republicans could be drawn into politics instead of violence.
And they were prepared to go quite a distance to keep them happy, considering special Army passes for leading Republicans, and keeping lines of communication open even after policemen were shot and bombs exploded by the IRA.
But in the end Republicans came to accept that British withdrawal was not on the agenda, the cease-fire collapsed - and a new leadership prepared to take over Sinn Féin and the IRA.
Relations between Dublin and London hit a low during 1975.
The British attempted to cover up exactly what they were up to with Republicans, but eventually had to come clean for fear that they would be, as one official put it, "rumbled".
There was a series of rows over different topics, with the British taking particular offence when FitzGerald urged people in Derry to put pressure on the Government to get a "fair share" of European funding for the North.
Using the ongoing deliberations of the Constitutional Convention as an excuse, Northern Secretary Merlyn Rees refused to meet FitzGerald for most of the year.
Meanwhile, the two Governments were also arguing over a more valuable prize - who owned the sea between and around the two islands.
With inflation rates heading for 25%, officials were comparing Ireland to Argentina.
The Government had to take tough action with unions to stop wages spiralling out of control.
The mixture of threats and inducements deployed by Finance Minister Richie Ryan and his colleagues are revealed for the first time - as is the story of how the Government was in danger of suffering humiliation during an unofficial strike by petrol tanker drivers seeking a 60% pay rise.
The kidnapping of Dutch industrialist Tiede Herrema at the end of 1975 by a breakaway Republican group tested Cosgrave's government, with its 'Law and Order' reputation.
The Government insisted it could not accede to the kidnappers' demands for the release of prisoners - but what would the consequences be if its 'hard line' led to a man's death?
As 1975 opened, so did Ireland's first Presidency of the EEC. It was a big challenge for a small country - especially as the most immediate item on the agenda was the British threat to withdraw from the Community if it didn't get concessions.
If Britain went, Ireland would lose out whether it left with its nearest neighbour or remained behind in the EEC. But skilful Irish diplomacy helped give Harold Wilson enough concessions to stay, as well as proving that a small country could perform as well as any of its partners in a demanding role.