“The Water Runs Deep in The East” is the first iteration of the Underlord Saga and follows Wei, Rayne and Iseul to defeat tyrannical Underlord Kartika.

The Underlord Saga begins with Kartika being the first to reform, regaining his consciousness in the Dujiangyan. He terrorises the landmark where Wei's excursion is taking place. Wei's powers act instinctively, allowing him to escape.

Rayne watches the tragedy unfold on TV at home in Wales but is surprised their school is going on a trip to China next week. When he arrives, Rayne and Wei fatefully meet. They encounter Kartika who retreats for the time being.

However, ISID member Sylvester Stylar identifies Kartika and mentions him going to North Korea. Sylvester also learns about the boys and offers to reward them if they helped him take down.

The boys find Kartika in North Korea and also Iseul, who agree to help them defeat Kartika. Kartika is defeated by Wei when he controls his shadow, then instantly blowing up from Rayne's bubbles.