Kara must fight her way across universes and lifetimes to find the mastermind behind her current troubles.[src]
In this issue it is revealed that the apartment building Kara lives is named, Hammersmith Tower, and her apartment number is 4-A. In the comics, Hammersmith Tower was the clockfaced building, where Kara lived with Lana Lang.
Kara's dreams are references to several storylines featuring the character:
In the first sequence Kara fights the wolves of Nightflame in a place called Innerworld, a reference to a Supergirl story published in Adventure Comics #421 (1972).
The second sequence alludes to a plot featured in the fifth volume of the Supergirl series (2005-2011), which unlike the TV show, depicts Kara as a teenager. Part of the fifth volume was written by Sterling Gates (issues #34-#59).
Kara mentions another dream, in which she is "an angel with wings of fire". This is a reference to the fourth volume of the Supergirl comic book series (1996-2003), where that version of Supergirl became the Angel of Fire on Earth.
The second sequence is a reference not to a Supergirl comic but to Superman #181 (1965), which features a story titled "The Superman of 2965!".
The two versions of Supergirl that Kara fights are references to the Red Lantern Supergirl, featured in the sixth volume of the Supergirl series (2014) and the Linda Danvers version, featured in the fourth volume (2000-2003), respectively.
Kara's last dream is a reference to the version of the character that appears in the digital series DC Bombshells, set during World War II.