The spy had guessed accurately. That was what Jiang Yi had planned to do.
The hostages had to be rescued, but he was not going to be the one to rescue them. He left behind the seal stone so that Heavenly King Wei and the others would go to the Longtan Mystic Realm. If they went there, Phantom King, Earth Emanations Sovereign, and Wintry Sovereign would be safe.
Of course, there was a condition to that: Dao Nù and Dao Leng could not kill the three of them. That was why he had to come to the Longtan Mystic Realm as well. He also had to lure Dao Nù and Dao Leng away, so that it would be easier for Heavenly King Wei to rescue the three of them. If Dao Nù and Dao Leng were not in the Longtan Mystic Realm, the people in the mystic realm would not dare to kill the three sovereigns. The Phantom King and the others would then have a higher chance of survival.