After reading the letter, he got a good grasp of the situation. He never expected to get help from that girl.
After poisoning him, the guy in a black jacket and other members of the Dark Raven Organization was supposed to help the guy who poisoned him leave the Imperial State with teleportation. If she hadn't stopped them, then Mad Beast Emperor would've never known about the true culprit.
Daniel had already told him about the culprit. And, also his master returning empty-handed. But, he was still able to find the culprit. It turns out Alena was the one who helped them stop the culprit from getting away from the Imperial State.
She also hinted to meet him after the end of the tournament which was not so surprising since she betrayed them only to please him.