Into The Astral Plane is the twelfth episode of ThunderCats 2011.
After mastering Sight Beyond Sight, the ThunderCats race back to the Elephant village to find the stone they seek, only to realize in horror that Grune and the Lizards had gotten there first and are holding the inhabitants hostage. In a back-story flashback, Tygra remembers the time when he was a young palace guard stationed at the gate. It is during his guard duty as a cub where he met Cheetara for the first time. She asks him to show her where the clerics reside. Tygra is enamored by her and stutters, but can't form a real response. She playfully tells him that she doesn't speak gibberish and assures him that she will find the clerics on her own. In a flash, she runs past him and across the courtyard up to the palace steps. Tygra chases after her and finally is able to speak to her. He brings her to the residence of the Clerics of Jaga. He tells her that they only accept the best and he wishes her good luck. Tygra watches Cheetara from a window as she is tested. She runs the obstacle course in record time but is impatient to finish quickly and fails the final obstacle because she didn't wait to see when the way would be clear. Jaga tells her that she has speed but not patience and tells her to go. Cheetara promises them that she won't give up and that she will wait until they accept her. She says that she has nowhere else to go and that she has no one to return to. She sits on the steps of the cleric building and waits.
Tygra reflects back on how he always did what their father wanted. He studied military history, he took an active role as a palace guard, and he performed his princely duties within the palace while Lion-O goofed off. Tygra is resentful that no matter what he did, Lion-O was entitled to the Sword of Omens simply through his bloodline alone, not through his deeds. Lion-O never had to earn anything. Lion-O makes a comment that Cheetara will choose him for the same reason that the sword chose him. Tygra reveals that, like the sword, Cheetara will be yet another thing that Lion-O doesn't deserve.
In the village, Grune becomes increasingly annoyed at the Elephants' short-term memory problem and threatens to kill them by nightfall should they continue to try his patience. Outside, Lion-O plans to wait until nightfall to do a surgical strike on the enemy considering the hostage situation while Tygra wants to just charge in with the ThunderTank blazing. He gets angered when Cheetara sides with Lion-O, and she was surprised by Tygra's suggested attack, since she always thought stealth was Tygra's specialty. He mutters to himself that that's probably why he was always invisible to her. In a second flashback, Tygra is seen leaving a white flower next to Cheetara, who is still waiting outside the clerics' door. She notices the flower and sees Tygra in the distance. She smiles at him and just as Tygra is about to walk toward her, Jaga returns and he continues to hide. Days pass and Cheetara is still waiting outside to prove herself to the clerics. Tygra hides in the distance as Jaga walks up to Cheetara. Jaga catches her as she is about to collapse and he tells her that she does have patience after all. He picks her up and carries her inside the clerics' compound and tells her that she is accepted into the clerics.
As they sneak through the brush, Lion-O displays his annoyance of Tygra's constantly challenging him at everything ever since they were cubs, but at the same time it also worries for him. Cheetara tries to reassure him that "Tigers are known for their pride", but Lion-O says it is much deeper than that and he senses some sort of "darkness" within his older brother. Cheetara responds that it is probably due to having always lived under his younger brother's shadow.
After taking out the surrounding guards, they close in on the village, but when Grune threatens to kill Aburn, WilyKit blows their cover in an attempt to stop them. The ThunderCats were forced to disarm themselves to keep the hostages alive, then Grune demands for Lion-O to tell him where the stone is, where he mockingly asks if he tried checking the hut. At that time, Tygra stealthily slips away. Grune once again threatens to kill the Elephant hostages, but Lion-O tells him where it is, in the Astral Plane. He makes Lion-O open the portal leading there with the Sword of Omens. Once opening it, Grunes orders the Lizards to kill the Elephants anyway. Before they can, they get blown away by missiles fired from the Thundertank, driven by Tygra. Cheetara can't believe what she was seeing, neither could Panthro, who was more annoyed that Tygra was driving the Thundertank without his permission. In the confusion, the Cats reclaim their weapons and fight back. After a serious beating, Grune quickly retreats once realizing the odds were not in his favor.
Once they were gone, the Cats stood before the portal to the Astral Plane. The Elephant Anet warns Lion-O that the Astral Plane is an unstable place and that he should be careful when trying to find the stone. When Cheetara gives Lion-O a kiss on the cheek for luck, Tygra gets angry and demands that he go as well. Seeing that he won't take no for an answer, Lion-O takes him up on it. Tygra enters the portal first. Just as Lion-O was about to follow, Anet stops him to give him a warning. He just saw a shocking vision: by the time the next day is over, Lion-O will experience a betrayal by Tygra. Lion-O doesn't believe it, saying that even if they don't get along well, he's sure Tygra wouldn't go so far as to betray him. Aburn tells him that Anet's visions are never wrong, which doesn't help Lion-O's confidence before entering the portal. After the two Cats went in, Mumm-Ra in raven form, having been spying on the group the whole time, flies into the portal without notice.
- It's shown that Tygra first met Cheetara long before Lion-O did.
- This episode reveals how and why Cheetara joined the clerics.
- The swinging blades that Cheetara runs through in this episode bear a striking resemblance to the swinging blades that Wilykit faced in the ThunderCats (original series) episode The Tower of Traps and like Wilykit, Cheetara also trips and falls at the last blade.