S04E23 — The Vanishing (1)

Donald and Douglas reveal that they have built an upgrade for all the students bionics, except for Leo's. But the upgrade doesn't work on Adam, Bree, and Chase because their systems are older. Adam, Bree, and Chase are therefore left at their level, while all the students are much more powerful. Meanwhile, Daniel is brought to the Academy because he had been using his bionics in the outside world. Douglas decides to enroll Daniel at the Academy, and he makes Leo his mentor. Leo steadily tries to teach Daniel, but Daniel proves to be unteachable, so Leo gives him the upgrade as well. The students steadily start to vanish, including Daniel. Giselle Vickers, Douglas' old girlfriend, is revealed to have captured them. Daniel sends a video message to the Island, requesting help.