Complex sentence: More seriously, Bothwell was arrested on witchcraft accusations-of trying to arrange the king's death through sorcery-on 15 April 1591, and warded in Edinburgh Castle, formal charges being laid before the Privy Council on that day and the 21st.
Split into simpler sentences: More seriously, Bothwell was arrested on witchcraft accusations on 15 April 1591. Charged with trying to arrange the king's death through sorcery he was imprisoned in Edinburgh Castle on 15 April 1591, the formal charges being laid before the Privy Council on that day and the 21st.