Trussell then joined up with Queen Isabella and Mortimer in Paris before moving to Flanders where he was allegedly tasked with helping to build an invasion army by William I, Count of Hainaut. Trussell accompanied Isabella and Mortimer when they landed in England on 24 September 1326 at the start of their invasion of England. Their forces consisted of approximately 1500 soldiers, many of whom were Flemish mercenaries and others exiled Contrariants. Opposition was almost non-existent and so many barons, sheriffs and knights joined the rebellion that control of the country was secured within two months. Adam, Abbot of Glastonbury hid Despenser and the Lord Chancellor, Robert Baldock in Glastonbury Abbey, and in December 1326 Trussell was ordered to bring the abbot before the next Parliament. Both Despenser and his son Hugh Despenser the Younger were captured and Trussell oversaw the trial of the elder Despenser where he was denounced and sentenced to death. Both Despensers were gruesomely executed.