"In Search of Lost Time" is the ???th episode of Supergirl. It aired on April 23, 2018."In Search of Lost Time" is the fifteenth episode of the third season of Supergirl and the fifty-seventh episode overall. It aired on April 23, 2018.
M'yrnn inadvertently causes psychic disturbances at the DEO; Supergirl must work with J'onn to contain the chaos; Mon-El begins training Kara in fighting techniques he's learned in the future.
This is the episode that Mon-El gets his comic book accurate suit.
J'onn having had an imaginary friend from a parallel dimension named "Zook", a reference to the DC comic book character that appeared in comic books published by National Periodical Publications (now known as DC Comics) in the 1960s. He was the partner of the superhero J'onn J'onzz, the Manhunter from Mars (now known as Martian Manhunter). Zook's first published appearance was in the story, "The Invaders from the Space Warp" from Detective Comics #311 (January, 1963).
The title is a reference to the novel of the same name by Marcel Proust.
Kara uses the line "The son becomes the father and the father the son" from Superman.
The electric batons that Alex uses near the end of the episode may be a nod to Nightwing's enhanced Escrima Sticks, from the comics.