A man failed to appear before Oxford Crown Court because he had taken his cellmate hostage.
The 22-year-old had been due to appear to make plea on a robbery charge before a judge on December 6.
But the case had to be adjourned in his absence because of the hostage situation unfolding at Woodhill Prison in Milton Keynes.
A Prison Service spokesman said the hostage ordeal ended peacefully.
"Both prisoners are now in segregation and an internal Prison Service inquiry has begun," he added.
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