Lost Girl is the series premiere and the first episode of Justice League: Knights of Rao.
- Superman / Clark Kent / Kal-El (first appearance) (Flashback and main story) (joins Blue Lantern Corps)
- Terra / Tara Markov (Flashback and main story) (identity revealed)
- Lois Lane (first appearance)
- Justice League
- Batman / Bruce Wayne (first appearance) (flashback and main story)
- Green Lantern / Hal Jordan (first appearance) (flashback and main story)
- Flash / Barry Allen (first appearance) (flashback and main story)
- Martian Manhunter / J'onn J'onzz (first appearance) (flashback and main story)
- Wonder Woman / Diana of Themyscira (first appearance) (flashback and main story)
- Brion Markov (first appearance)
- Amelia Markov (first appearance)
- Vandal Savage (first appearance) (flashback and main story)
- Lex Luthor (first appearance) (flashback only)
- Joker (first appearance) (hologram only)
- Cheetah / Barbara Ann Minerva (first appearance) (hologram only)
- Sinestro (first appearance) (hologram only)
- Professor Zoom / Eobard Thawne (first appearance) (hologram only)
- Rose the Ravager (first appearance) (flashback only)
- Lara Lane Kent (first appearance)
- Ronnie Raymond (first appearance) (flashback only) (dies)
- Professor Martin Stein (flashback only)
- Teen Titans (mentioned only)
- Viktor Markov (single appearance) (flashback only) (dies)
Determined to redeem his failure to stop Vandal Savage's destructive rampage, indirectly caused by Lex Luthor's framing of him, Superman looks after and trains Tara Markov, the young daughter of the currently deceased Viktor Markov, to become the heroine she wanted to be.
It all starts with Superman standing in the middle of a graveyard in front of the grave of Ronnie Raymond. Small flashbacks reveal that Superman and his fellow Justice Leaguers were infamously framed by Lex Luthor for crimes they did not commit. The heroes' names were eventually cleared out of the charges, but not before Vandal Savage managed to wound Firestorm in a National Congress, causing an explosion which killed him with numerous people, leaving only Raymond's merging partner Professor Martin Stein alive. Just then, Superman spots from the distance a young girl running in the desert and recognizes her as the daughter of Viktor Markov, the king of Markovia who was among Savage's victims. Determined to save at least one life he could not save that day, Superman, caring a star he collected where Raymond perished, flies there to help her.
Following the events of Terra in Teen Titans, Terra is still running in the desert and feeling torn between the decision of either getting help from the Titans or working for their nemesis Slade to help her control her malfunctioning powers. Just then, she is confronted by Slade, who still tries to convince her to trust him and that the Titans are "the true enemy". But before he can get any closer, Superman storms in and backhands him, forcing him to retreat. Superman eventually convinces Terra that Slade is lying and is only trying to use her for things she never really wanted to do. He proves this right by giving her the star he found. The star eventually grants her full control of her powers when it restores the one thing which was missing in her: her memories. She eventually remembers her real name as Tara Markov and that Slade's daughter Rose had been hired by Savage to capture her and brainwash her, although Tara barely escaped her fate.
Though happy to remember everything, Tara is still devastated with what really happened. Superman comforts her and takes her home, where she is reunited with her brother Brion and their mother Amelia. Superman takes his leave, but not before he is allowed by Amelia to come back to train her and Tara shares with him a piece of the Markov Family's power, granting him the abilities to control Crystal at will. Next day, after teaching her new ways to use her powers, Superman takes Tara to the Watchtower, where he gives her a small trip before he answers a distress call from the Justice League about Savage, who had stolen newly developed Lexcorp weapons and is attacking Washington D.C.. Superman eventually allows Tara to use the Costumizer Machine to craft for herself her own Superhero Costume and the V.R. Computers to make herself ready to battle the threats the Justice League and the Titans fought against.
Tara uses the Costumizer to craft for herself a one shoulder red and white leotard with large blue boots, golden belt, bracelets, necklace and leg rings and a red mask and uses the V.R. Computer to practice her abilities by battling and defeating virtual images of the Leaguers' primary villains (Lex Luthor, the Joker, the Cheetah, Sinestro and Professor Zoom) one by one. Right after helping the League stop Savage's plot and watching as Tara leaves for home through the Teleporters, Superman bids his teammates as well as his wife Lois and their daughter Lara a short farewell and vows to come back when he regains his sense of honor. Back in Markovia, Tara is allowed by her family and Superman to roam free as long as she stays out of trouble and out of the villains' sight. Tara agrees to do so as she also vows to humiliate every tyrant in the world, letting Superman agree with the truth she knows: that too much tyranny is the real threat affecting Earth. She and Brion later watch as Superman puts on a Blue Lantern Power Ring before departing to Odym, where he would find the strength to forgive himself. Tara properly vows to do what it takes to help reform her mentor's honor. Superman overhears what Tara says and voices his belief with a smile. After Superman leaves, Tara admits that what she just swore to do will be too much for her to handle alone (especially after her first day with the Titans having not ended well), which is why she is determined to be bringing a team together to honor Superman and the Justice League and join the work they started.
- George Newbern as Superman / Clark Kent / Kal-El
- Ashley Johnson as Terra / Tara Markov
- Dana Delany as Lois Lane
- Grey DeLisle as Wonder Woman / Princess Diana of Themyscira
- Kevin Conroy as Batman / Bruce Wayne
- Phil Morris as Vandal Savage
- Ron Perlman as Slade
- Josh Keaton as Green Lantern / Hal Jordan
- Wally Wingert as the Flash / Barry Allen
- Carl Lumbly as Martian Manhunter / J'onn J'onzz
- Jason Marsden as Brion Markov
- Tara Strong as Lara Lane Kent
- Kari Wahlgren as Amelia Markov