Try going back to the alchemist and talking to him again. Perhaps going through the speech options about this quest again will trigger the cut scene.
Did you notice that the triangular teleporters point to the direction they will send you?
hint <span class='standouttext'>Spoiler : </span><span class='spoiler'>When you are on the mainland, the eastern island teleporter is pointing to the western island...</span>
major <span class='standouttext'>Spoiler : </span><span class='spoiler'>Use the triangular teleporter to get to the eastern island and drop a teleporter pyramid there. Take the teleporter pad back to the mainland, and use the other teleporter pyramid to get to the eastern island, without changing that triangular teleporter's orientation. Tossing a teleporter pyramid onto the eastern island directly might work also, but I didn't try that.</span>
