Short answers, pulled from the story.
The Prayer Book Rebellion, also called the Western Rising, was a popular revolt in Cornwall and Devon in 1549. It broke out against the introduction of the first Book of Common Prayer, which replaced Latin church services with an English-language liturgy.
The Prayer Book Rebellion took place in 1549, beginning at Whitsun when parishioners in Sampford Courtenay, Devon, refused to use the new prayer book. The rebels were defeated and their leaders executed about two months after the fighting began.
Up to 5,500 people died in the Prayer Book Rebellion, most of them Cornish and Devonian Catholics. Casualties included about a thousand rebels killed at the Battle of Clyst St Mary and roughly 900 bound prisoners killed at Clyst Heath.
The Cornish rebels were led by Sir Humphrey Arundell of Helland and John Winslade of Tregarrick, alongside Bodmin's mayor, Henry Bray. In Devon, parishioners from Sampford Courtenay marched on Exeter, gathering further Catholic support along the way.
People in Cornwall and Devon rebelled because the new English-language prayer book replaced services many wanted kept in Latin, and in Cornwall it displaced the Cornish language too. Poor economic conditions, including a new poll tax on sheep and quadrupled wheat prices, deepened the anger.
Edward Seymour, 1st Duke of Somerset, sent Lord John Russell to suppress the Prayer Book Rebellion with a royal army. Russell's forces defeated the rebels in battles at Fenny Bridges, Clyst St Mary, Clyst Heath and Sampford Courtenay, and rebel leader Sir Humphrey Arundell was later executed for treason.