Granddad John Hill thought he'd hit the jackpot when he spotted a silver ring on the ground while out metal detecting with his grandchildren.
But when he put his finger into the ring, his blood ran cold – and then he shouted: "RUN!"
For the ring wasn't some precious relic – but attached to a pin, which was attached to a Second World War hand grenade!
John's grandsons James, 14, Dylan, five and Sidney, two, had gathered round to take a look at what he had found before the 67-year-old realised they were in danger.
After the boys scarpered, super-calm John then placed the grenade carefully on the ground before dashing a safe distance away and dialling 999.
A Royal Navy bomb disposal team were called to farmland in Sampford Peverell, Devon, where they detonated the live hand grenade in a controlled explosion.
History enthusiast John, a sites officer for the East Devon Metal Detecting Club, has discovered various explosives in the past - but never nearly triggered one.
The grenade was found 10 inches beneath the ground close to the Grand Western Canal where a soldier possibly dumped it after retuning home from the Second World War.
John, from Tiverton, Devon, said: "I picked up the ring but there was a grenade attached to it. It is quite exciting, but not if you have three young children with you.
"I told the grandchildren to run as it could have gone off. They occasionally turn up. This must have been dumped in the canal and dredged out.
"But once it is up and exposed, somebody could have walked over it or a tractor which was ploughing could have had its back end blown off."
The remains of a Canberra bomber that crashed in 1961 were also recently found nearby, including an ejector seat.
The controlled explosion was witnessed by Grand Western Canal ranger Craig Saunderson, who felt the blast from 100 yards away.
Craig, who has served with the South African Marines, said: "We saw the puff of smoke and felt the shockwave from the other side of the canal. It was quite good actually.
"They placed a small explosive charge over the grenade and laid a line which was connected to the detonator. It was quite an explosive end to the day, to say the least."