Tekzhu and Zhenya

Taekju is an ordinary guy, the son of a healer. Since childhood, he has studied herbs and medicines and tested the effects of poisons on himself. He lived in poverty in a dangerous district.

Evgeny (Zhenya) is the younger son of the previous emperor and a possible heir to the throne. White hair, blue eyes. An expert swordsman. He is always accompanied by his loyal advisor, Caesar.

The Emperor is the eldest son of the previous emperor. Calm, wise, and just.

Irina is a painter and poet of the inner court, a kind friend of Taekju.

Vanya and Ivan are guards. Ivan is calm and rational, while Vanya is energetic and constantly seeks adventure.

Concubines: Idia — kind and welcoming;
Rai — calm and perceptive;
Darina — the youngest, trying to appear more mature;
Mitsuya — mysterious and cold.

Egor is a blacksmith, Arthur is his assistant.

Plot

While gathering herbs, Taekju is kidnapped and sold to the palace. At first, he works as a simple servant, then he meets Irina, and they become friends.
Soon, Idia gives birth to a daughter, and Rai to a son, the heir. However, both children fall seriously ill. The heir dies after a week, and Rai, unable to bear the grief, falls seriously ill herself. Idia's daughter also finds herself on the brink of death.
Taekju begins an investigation and discovers that the cause is the powder used by the women of the palace. It contains a poisonous mineral that is especially dangerous for children.
Not wanting to reveal himself, he writes just two words on a scrap of fabric at night: "Powder. Poison." and leaves it on the palace porch. The note is found by Zhenya, who begins a search for the person capable of writing it, as literacy in the palace is supposed to be limited to the emperor, himself, Caesar, and the concubines.