The new episode of CW's "Supergirl" featured ex-lovers Mon-El (Chris Wood) and Kara Danvers (Melissa Benoist) sharing a special moment, not to rekindle their past romance but to train together in hopes of defeating the Worldkillers. Season 4 has seen the rise of a Wordkiller known as Reign (Odette Annable), and with another powerful ally by her side, Kara needs to work harder to stop the villains from destroying the planet.

The synopsis for "Supergirl" season 4 episode 15, titled "In Search of Lost Time," revealed that Kara was trained under the supervision of Mon-El. The Daxamite royalty has learned a fighting technique in the future, which was effective in bringing down the Worldkillers in that timeline. Unfortunately, the training takes a wrong turn as Kara and Mon-El were seen having a heated exchange of words. 

Fans also saw some exciting changes in "Supergirl" season 4 episode 15, including Mon-El's new suit. The character's new appearance complemented the design of Kara's Supergirl costume. Those familiar with the original DC comic book material would easily recognize Mon-El's new red and blue suit, except for the rectangular gold attachment that replaces the rounded and oversized button. 

"Supergirl" season 4 episode 15 also featured some psychic disturbances at the DEO. Together with J'onn (David Harewood), Kara had to stop M'yrnn causing more destruction inside the DEO.

Fans saw Reign, together with her sister and another Wordkiller, Purity (Krys Marshall), going on their mission for dominance. The two also aimed to find the last known Wordkiller on Earth, Pestillence.

"Supergirl" season 3 episode 15 aired April 16 on The CW.