- Guardians of the Galaxy
- Snow Leopard / Sally Avril
- Baxter Institute
- Tigra / Mary Jane Watson
- Beast / Hank McCoy
- Dora Skirth (first appearance) (joins team) (leaves Life Foundation)
- Venom Symbiote (First appearance)
- Life Foundation
- Carlton Drake (First appearance)
- Norman Osborn
- The Goblin (illusion only)
- Venom / Alistair Smythe (First appearance) (single appearance as Venom; gets and loses Venom Symbiote)
- Norman Osborn
- Taserface (first appearance)
- Kree Empire
- Ronan the Accuser (mentioned only)
- Unnamed Sakaarians
- Mr. Fantastic / Reed Richards (mentioned only)
- Midtown High School
- Ashley Kafka
- Maxine Joan (cameo; unnamed)
- Eddie Brock (first appearance) (cameo; unnamed)
One week after their first teamwork, the Guardians of the Galaxy (Nathan Quill / Star-Lord, Zoe Gillan / Gamora, Sebastian Allan / Rocket Raccoon, Drax the Destroyer, Groot and Yondu Udonta) have become universe-renowned heroes after travelling around the galaxy protecting innocent aliens from hostile forces, such as a crew of space pirates led by Taserface, and an army of Sakaarians attempting to ravage the Skrull homeworld under Ronan the Accuser's orders, although Nathan and Zoe are still remaining on Earth to continue their normal lives with their families and their studies at Baxter Institute. During which, Zoe senses a familiar presence on Earth and seeks to investigate. Nearby, a cat breaks out of Oscorp, scaring away the guard dobermanns.
The cat walks around New York City, where more dogs are terrified of him before encountering Zoe with Sally Avril / Snow Leopard. Zoe soon recognizes the cat as Cougar, her childhood friend and a alien Flerken she bonded with, and they embrace. Through their symbiotic, psychic link, Zoe learns that Cougar has been teleported from his home-planet of Glxx to Earth by a small prototype of the Space Stone which was tested on Oscorp by Alistair Smythe for future projects. Knowing that neither Norman Osborn nor any scientist in his employ can be trusted to own any alien artifact due to numerous incidents associated to Oscorp, Zoe (posing herself as a Oscorp intern) rushes there to gather more evidences and confiscate the Space Stone prototype, eventually sensing there is another in New York. Meanwhile, Osborn and Smythe are at Life Foundation, where its CEO Carlton Drake and scientists are secretly experimenting on Symbiotes which were discovered from a meteorite extracted by another Space Stone duplicate which Oscorp's engineers sold for them. Osborn (unknowingly under Goblin's influence) agrees to exam the organisms, despite Life Foundation head scientist Dora Skirth's concerns over the possible disaster. Overhearing this, Rocket reports to the rest of the Guardians and informs them to be prepared, while a small duplicate of the Symbiote (designated as Venom) secretly possesses Smythe.
While she and Nathan are with Mary Jane Watson attending to a class chemistry lesson with Dr. Hank McCoy / Beast, Zoe (through Cougar) spies on the Oscorp engineers who are experimenting on the Symbiotes, as Osborn (again against Dr. Skirth's objections) opts in subjecting on prison convicts and homeless bystanders, while Rocket and Yondu set a small series of bombs in Drake's secret laboratory to destroy the other Symbiotes and the Space Stone prototype. Smythe begins displaying strange symptoms until the Symbiote in him manifests itself around his body as a monstrous creature which begins wreacking havoc around Oscorp by hijacking its combat robots to attack everyone, alerting the Guardians, Tigra, Snow Leopard and Beast. The heroes manage to evacuate the scientists and work to prevent the mutated Smythe from reaching the other Symbiotes. Gamora, Tigra and Snow Leopard are soon approached by Skirth, who tells them she knows a quicker way to stop the Symbiotes. Facing defeat, the mutated Smythe breaks the rest of the Symbiote out of its containment capsule and reabsorbs it, fully completing Venom's transformation, as Venom plots to get his revenge on Drake. Just then, Cougar (powered by Gamora's bond with him) changes to the form of a beastly lion/toger hybrid feline.
Star-Lord, Rocket and Yondu escort Drake to safety while Groot, Drax and Cougar hold Venom off. Gamora, Tigra and Snow Leopard reach Skirth's lab, where they create a concussive bomb made of Vibranium and Pyroclastic capsules, since Symbiotes have two known weaknesses: high-pitched sound waves and fire. Osborn attempts to be rid of the situation by preparing a super cannon to destroy both Venom and his opponents, but is stopped by Rocket as the girls and Skirth arrive and, after Groot, Drax and Cougar separate Smythe from the Symbiote, Gamora tosses the bomb at Venom, blowing him up and incinerating him, while Rocket detonates the bomb, destroying Drake's secret laboratory and the Symbiotes in it. As the Guardians (now officially joined by Cougar) are again hailed for saving the day, Skirth reprimands Drake for disregarding the chaos which the Symbiotes could have caused and decides to resign from her job in Life Foundation. Next day, Nathan, Zoe and Mary Jane have are back in the Baxter Institute, now joined by Skirth as a new teacher who teaches them more about symbiotic links. Meanwhile, the Space Stone prototype (still intact and functional even after the destruction of Drake's laboratory) ends up absorbed by a shy young girl after she inspects it, while the Venom Symbiote (which barely survived the explosion) is shown stalking an unemployed, angry man who is throwing darts at a picture of Drake in the walls of his room.
- Scott Menville as Star-Lord / Nathan "Nate" Quill
- Laura Bailey as Gamora / Zoe Gillan
- Ashley Johnson as Tigra / Mary Jane Watson
- Lacey Chabert as Snow Leopard / Sally Avril
- Troy Baker as Rocket Raccoon / Sebastian Allan
- Travis Willingham as Groot, Beast / Dr. Hank McCoy
- William Salyers as Yondu Udonta
- Danica McKellar as Dora Skirth
- Benjamin Diskin as Carlton Drake, Sakaarian Captain
- Kevin Michael Richardson as Venom, Taserface
- Jeffrey Combs as Norman Osborn, the Goblin
- Jason Spisak as Alistair Smythe
- Marisha Ray as Ashley Kafka, Drake's assistant
- The title is a reference to the song "The Lion Sleeps Tonight" by The Tokens.
- In the moment Norman Osborn observes the Symbiotes, the Goblin (invisible to everyone's eyes, but seen by the audience near a reflection of Osborn in a glass) has Osborn say "Well, I guess that's worth a look.". This moment is similar to the post-credit scene of the 2011 Thor film, where Loki did the same to have Erik Selvig agree to study the Tesseract's powers under Nick Fury's wishes.
- "The Ballroom Blitz" by Sweet
- ↑ following previous episode
- ↑ events of Feline Power
- ↑ events of previous episodes, since A Better Genius
- ↑ since Living Brainstorm
- ↑ the same seen in Living Brainstorm
- ↑ the two unnamed and unvoiced characters are identified offscreen as Maxine Joan (soon to be known as Singularity in the Season's final arc) and Eddie Brock (who returns as Venom in Back to Black) respectively