"Os" is the 16th episode of the third season of the American science fiction drama television series Fringe, and the 59th episode overall. The episode centered on the Fringe team's investigation into a series of robberies of the element osmium, which they connect to a scientist (Alan Ruck) who is able to defy the laws of physics. "Os" was written by Josh Singer and Graham Roland, while Brad Anderson served as director. Along with Ruck, the episode also guest-starred Jorge Garcia in a brief cameo as a security guard. On its first broadcast in the United States on March 11, 2011, an estimated 3.76 million viewers tuned in, giving it a 1.5/5 ratings share for those between the ages 18–49. Critical reception to the episode was generally positive, as multiple critics noted that Ruck was well-cast as a scientist just trying to help his son. Plot The Fringe team is called to the scene of a robbery of a metal depository; the body of one of the thieves, shot by a security guard, inexplicably floats off the ground, while a second culprit has gotten away. They find that the thief has taken off with a supply of osmium, one of the densest elements, and an autopsy later reveals that the dead thief's body is filled with the metal. Tracking a security card on the body, they enter a warehouse where they find the second culprit, dead, along with the bodies of several more people, all of them paraplegic. Walter (John Noble) notes that the physical properties of osmium (both gravitational and thermal) have been reversed, and by melting the osmium collected from the first victim using liquid nitrogen, they detect the presence of the rarer element lutetium, typically only present in meteorites. Recognizing that the local science museum has a display of meteorites, the Fringe team is able to secure Dr. Crick (Alan Ruck), the man behind the osmium injections, and another paraplegic who has taken Dr. Crick's injections as they attempt to steal the display. With Dr. Crick in custody, Walter learns that the man had worked in aerospace to find an alloy for fighter craft. He happened upon the combination of the osmium-lutetium alloy that generated a material lighter than air, and sought to refine a permanent solution to give his own paraplegic son the ability to walk, having promised the same to those that had died from