The Ninja Left Behind.

Shortly after Chen is defeated, Garmadon isn't sent to the curse realm, the ninja and Wu leave to do training, leaving Kai to defend Ninja alone. But, Kai had learned something the morning they left and when he tried to tell his boyfriend Cole, Cole told hem it could wait till they returned.

They left twelves years ago, Kai has moved on and had to leave being a ninja for a few years. Now the Ninja and Wu are back, what awaits them when they find Kai again. Read and find out.