The murky world of terrorist killers and military intelligence in Northern Ireland is explored in several papers.
The Sunday Times says the agent known as Stakeknife, who is now said to be in hiding, was regarded by the British military as the jewel in its crown.
He is said to have penetrated the highest ranks of the IRA and his intelligence was apparently read at cabinet level.
The Times believes his cover has been blown by a disaffected former agent, who has accused Whitehall of reneging on a promise to give him a pension and resettlement package.
'Blair battles Brown'
The Sunday Telegraph says the prime minister has authorised his cabinet colleague, Helen Liddell, to challenge Chancellor Gordon Brown's expected verdict that Britain is not ready for the euro.
The Sunday Mirror says a campaign to turn up the pressure on Mr Brown to agree to a referendum is being co-ordinated by Number Ten.
The Observer agrees and reports Mr Blair is to allow cabinet members a freer rein to push the arguments for joining the single currency.
A former chairman of the Commons treasury committee, Giles Radice, tells the Independent on Sunday the stand-off will determine which of the two men is actually running the government.
Mr Blair has secretly agreed to share sovereignty of Gibraltar with Spain in return for Madrid's support for the war in Iraq, claims the News of the World.
According to the Sunday Express, the deal was stitched up at the summit meeting in the Azores attended by the British and Spanish leaders and President Bush before hostilities began.
The Sunday Times says documents, allegedly recovered from an office of the Iraqi intelligence service, suggest Saddam Hussein's agents tried to infiltrate the Arab satellite news channel, Al Jazeera.
The intention, says the paper, was to subvert the station's coverage.
Al Jazeera denies that its reporting on the crisis in Iraq was biased or that it operated on behalf of Baghdad.
After the acres of newsprint devoted to Tony Blair's half-century, stand by for the next Big Birthday - Prince William's 21st.
A taste of what we can expect in the run-up to his coming of age next month is provided by the Express.
The Queen, it confides, is becoming increasingly worried about the prince's growing reluctance to perform royal duties.
The Mirror says guests invited to his birthday bash at Windsor Castle have been asked to dress as characters from the film, Out of Africa.
The Sunday Telegraph reproduces a set of stamps bearing photographs of the prince - and the first coin to be struck in his image.
The People says the Home Secretary, David Blunkett, plans to increase the fee for checking whether people working with children have any convictions for sex crimes.
It believes the proposed hike from £12 to £35 could virtually bankrupt schools, hospitals, care homes and churches.
Fair or foul?
Beneath the headline "I'm a stick insect, get me out of here", the Independent says the reality TV show - in which celebrities have to endure life in the jungle - has fallen foul of animal lovers.
It says 68 viewers have complained about the treatment of the creatures used to terrorise the contestants.