I forget the title of the novel, but I vaguely recall this detail: A bunch of heroes are summoned into a world and are living in the palace as they train, but the main protagonist finds out that the king is planning to kill them.
I know a series that sounds similar The Demon General of Earth (♀) Was Ridiculed as “The Weakest of the Four Heavenly Knights”, but After She Decided to Quit the Demon King’s Army and Lead a Slow Life, She Was Forced to Live With the Exiled Hero (♀) … Also, for Certain Reasons, They Got Married. Is this it?
My Status as an Assassin Obviously Exceeds the Hero’s - maybe? I only read a few dozen chapters so I don't know how it turned out.