Over in Rome, Pope Gregory VII was embroiled in the Investiture Controversy with Holy Roman Emperor Henry IV. Although Henry's penance was made prior to 1082, there were still arguments over who gets to invest clerics, the Church or the secular powers.
Odo gathered his Kentish forces and planned a military expedition to Italy. Why would he do this? The following is conjecture. Perhaps it was the Holy Roman Emperor's hostility to the pope that gave Odo an idea. Historians writing a couple decades later said Odo wanted to be pope. Either he would take an army to support Henry, who might then support Odo as pope, or possibly he thought he could bring his own army to Gregory's defense and be named his successor for the effort. In 1080, Henry declared Gregory deposed and installed his own pope, Antipope Clement III.
All we know is that Odo was prepared to take a large number of English—Saxon and Norman—subjects out of the country and march across other countries to engage in war with someone, and William wasn't having it.
In 1082, William had Odo imprisoned on the continent, where he spent the next five years. He remained Bishop of Bayeux (his seal is depicted above), but William took back all lands in England and the title Earl of Kent.
In 1087, William was on his deathbed. William's other half-brother, Robert of Mortain, persuaded William to forgive Odo, who was allowed to return to England. Unfortunately, he made another choice to back the wrong horse. William had made his eldest son Robert Curthose, the Duke of Normandy, and the second son William Rufus was made King of England. (Normandy was far larger than England.) Robert also wanted England, and Odo decided to support him.
The rivalry between William and Robert turned into the Rebellion of 1088, and that's where we will pick up the story tomorrow.
As for Odo, he joined the First Crusade and died on the way, in Palermo in early 1097. He was buried in Palermo Cathedral.