 In 1455, Prince Suyang (one of Sejong's sons) forced the young King Danjong, his nephew, to abdicate, taking the throne instead as King Sejo.Following secret orders from his father Seong Seung, Seong Sammun along with Bak Jungrim, Bak Paengnyeon and others plotted to assassinate the new king and restore King Danjong to the throne.The plot was exposed and the plotters all arrested.