Soon after King Richard II's deposition in 1399, his relatives and old friend, the Earls of Kent, Huntingdon & Salisbury met at the house of the Abbot of Westminster and plotted to institute an insurrection in the New Year which would place the imprisoned monarch on the English Throne once more. The so-called 'Oxford Conspiracy' was welcomed in Berkshire by men such as Sir Bernard Brocas of Clewer. Boosted by such support, the party even revealed their plans to the seven-year-old Queen Isabella when they visited her in confinement at the Bishop of Salisbury's palace in Sonning, but, in the end, little came of all their plotting.

Richard's once banished cousin was by then the self-proclaimed King Henry IV. He was scheduled to attend a Royal tournament at Oxford, but soon discovered that he was in much danger there and came down to Windsor instead, to take possession of the castle. A lesser conspirator, the Earl of Rutland, had an uneasy conscience and, via his father, the Duke of York, had sent the new King a warning of impending events. The three leading Earls were betrayed. Travelling to Windsor disguised as mummers attending a New Year Tournament, they came to the castle gates, at nightfall on 4th January, with a company of some four hundred armed horsemen, many of them men of good rank, and everyone of them bent on taking the monarch unawares and killing both him and his sons. To their surprise the deceit was unnecessary and they entered the fortress unchallenged. But, despite an intensive search, including the canons' quarters, they found that the King had gone. He had ridden hard for London only a few hours before, when the Lord Mayor had arrived at the castle to confirm the approaching threat. In the City, King Henry quickly gathered an army capable of crushing the rebellion and had them camp on Hounslow Heath ready to intercept the conspirators on their way to London.

So Salisbury retreated westwards in open rebellion, while Kent and their followers held back Colnbrook and then Maidenhead where they were to attempt to buy some time by holding the bridge there. The Earl of Salisbury halted first at Sonning again to raise the hopes of the Queen by telling her the false story that her husband had broken out of prison and gathered about him a force of a hundred thousand men! The little girl eagerly consented to join them and took especial pride and joy in ordering the hated badge of Lancaster to be discarded by her attendants and her husband's White Hart adopted once more. He then entered Reading where he made efforts to raise further support before moving on to Wallingford, Abingdon and through the Vale of the White Horse, everywhere telling people to prepare to help King Richard. At Faringdon, he even offered the credulous country folk a the chance to look upon the monarch himself - his double, a priest by the name of Maudelen. 

By this time, the Battle for Maidenhead Bridge had already lasted three days, with Kent's rear-guard managing to even capture two packhorses, two baggage-wagons and a chariot from the King's army. The Earl eventually stole off quietly in the night and, having cleared Maidenhead of all provisions, took most of the townsmen with him to serve King Richard. The Royal forces therefore broke through their barricades and were soon hot on the rebel leaders' trail. Kent met Salisbury at Cirencester, but the citizens there were loyal to the new King and, headed by their bailiff, arrested the two men and detained them for a day and a half with the promise that they would be safely delivered up to Henry IV. However, there was a bungled attempt to rescue them and an angry mob of townsfolk had them both beheaded, along with their associate, Sir Ralph Lumley.