When night falls, we find peace in the knowledge that daytime will return soon, and vice versa. But what if the world was split: daytime and night are two different, coexistent worlds, each with it's own laws and rules. At dawn and sunset, our soul switches to inhabit our other being, our 'twin'.
Inside a mad scientists laboratory the PCs find a short creature with smooth, oily and whale like skin. The head is faceless and smooth also. But hundreds of white eyes on the PCs from the fat belly of this creature. The PCs are about to kill it as it speaks to them in a feeble but intelligent voice, asking them to pour the contents of a green vial on it. Will they do so? And if so, what will happen?