The Truth.

Valerian watched Imperium with a polite smile on his face. The young man leaned forward with the vial in both hands to commit to the act. He was genuinely projecting himself to be the humble person here. The crowd was already won over to his side, and Imperium was in a bind. 

Imperium found the situation to be forceful, but he was not worried. He was confident in his skills to get away from this situation. He said, "Young Monk, I will be obliged to accept this gift." 

Valerian nodded and passed him the vial. However, he was sure that Imperium would not give in too quickly, so he showed his other card, "Lord Imperium, this potion must be drunk within fifteen days from brewing. I am clumsy and can only refine it once in five trials. This one is in the last hour of its life. I hope you can consume it immediately and show generosity to the order of Mercy. 

The priests and the nuns from the temple here have put you in a great bind. I apologize sincerely."