Pearl returns to Artemis Island and is informed by Thomas that she will be inducted into the Golden Mean. But first, she must take a test that requires her to unlock a ‘Mystery Cube’.
She flies to Stockholm to meet her mentor Father André. First, they visit the Royal Academy of Sciences, and then an underground university in Warsaw where Madame Curie began her education. Her work will help Pearl unlock the cube.
They go to The Sorbonne in Paris, where Madame Curie also studied. Luc is there and Pearl mentions that she thinks she may be falling for him.
She then goes to a field hospital in Belgium, where Pearl discovers that Madame Curie built portable X-ray devices for use in field hospitals during the Great War. Pearl realizes that she must build an X-ray device to look into the cube with parts she has collected. She builds the device and sees that the cube has a gold ring inside.
They fly back to Artemis Island where Pearl is made a member of the Golden Mean and given the ring.