Experts from Bletchley Park are trying to crack a 250-year-old code rumoured to point the way to the Holy Grail.
Bletchley's experts are credited with helping to end World War II
Specialists from the Buckinghamshire code-breaking centre hope to decipher words etched on a garden ornament at Shugborough in Staffordshire.
The Shepherd's Monument in the grounds of the stately home displays an inscription that has never been solved.
Second World War veterans using the celebrated Enigma machine are joining Bletchley's current team of experts.
The code breakers are at Shugborough, the ancestral home of the Earls of Lichfield, on Tuesday.
Christine Large, Bletchley Park's director, said: "This is such an unusual challenge that my colleagues and collaborators, who include veteran code breakers and modern day decoding experts from Bletchley Park's 'offspring' GCHQ, cannot resist."
Shugborough's general manager, Richard Kemp, said: "The Anson family, who built the estate, commissioned the monument but it had unproven connections with the Knights Templars.
"The inscription is rumoured to indicate the location of the Holy Grail, which must rank as one of the world's great mysteries."
It is estimated that work carried out at The National Codes Centre at Bletchley Park in Milton Keynes helped to shorten the Second World War by two years.
The site is now a popular tourist attraction.