Peter (Joshua Jackson), after injecting the Observer implant in his own body, returns to Etta's safe-house to mourn her loss.

In the appropriate apartment, Walter follows instructions on the tape that let him enter the pocket universe where the normal rules of physics do not apply, with hallways running upside down or in vertical directions, as in a work of M.C.

Walter tries to remember where to look, but while trying to come up with this, he encounters a man named Cecil (Zak Santiago) who happened into the pocket universe while taking shelter from the Observer bombing.

The group finds the room, but it is empty, save a radio that is fused to a certain frequency, something that Walter did not give the boy in the past.

The audience is shown how the Observers "see" the world, using computer-like vision that is tinted blue and devoid of most other colors.

Captain Windmark watches this from afar, while high on a building behind him, a stenciled picture of Etta urges the humans to "Resist".

"Through the Looking Glass and What Walter Found There" was written by co-executive producer David Fury, while being directed by 24 vet Jon Cassar.

It also has many plot elements that draw on "The Navidson Record" from "House of Leaves.," a modern classic popular horror/sci-fi novel such as the use of super-8 video and a maze in a parallel universe.

An estimated 2.47 million viewers watched the episode, and earned a ratings share of 0.9 among adults aged 18 to 49, to rank fourth in its timeslot.

He commented, "Fringe gave us a good episode that puts another important piece of the puzzle in place and brings back an old friend.