This article may contain spoilers.

In what may be said is the mellowest episode to date for Defying Gravity, this weeks adventure focused on what it meant to cross the Rubicon; the point of no return.

For each of the Antarescrew, it held a different meaning: for Ted (Malik Yoba), it meant this was the last chance to return to Earth; for Donner (Ron Livingston), it meant it was time to let go of the past; and for Nadia, it meant realizing that things were never going to be the same again.

Explaining the origins of the term Rubicon, Nadia (Florentine Lahme) told the story of how during the Roman Republic, crossing the Rubicon River was an act of war, and that Julius Cesar had ignored that rule, crossed the river, and as a result, civil war was declared - all of which ultimately led to Cesars deification. It is hard to say whether this story is a foreshadowing of a civil war that may occur on the Antares, or whether it was merely to illustrate that sometimes once a line is crossed, there is no going back. But, as Donner summarized, Once we decide to cross the line, we live with the consequences.

For the bulk of the episode, Donner was literally haunted by the past. Whereas, in the prior episode he was drawn away from the ship by the ghosts of Sharon Lewis and Jeff Walker, this time Donner was given a vital clue by the hallucinations of the red Mars dust. He may have thought he was losing his mind, but in reality those visions are what saved them as one of the water filtration system tanks had an incorrect pH balance which could have killed them all.

Perhaps because Donner was clinging so tightly to his past, he was the one that Beta gave the vision to. Donner, more so than anyone else on the ship, has reacted to Beta. Ted is in denial and wants nothing to do with Beta; and Zoe (Laura Harris) only runs from the sound of the crying baby. Beta is perhaps reaching out to those it can communicate with in any way possible.

What Worked

One of the cooler elements of the episode was the time capsule. Ted had proposed having one, like the one that they had on the Mars Mission. Ted said it was necessary in order to promote unity by mutual sacrifice to bring everyone closer together, as they will need each other down the line. Despite Donners reluctance to do anything replicating that fateful mission, everyone begrudgingly complied. We learned that Paula (Paula Garces) is religious and was initially unwilling to part with a single thing from her past; we saw that Zoe had brought her mothers Tarot card of the Hanged Man (the meaning of which was never explained), and we learned the significance of the baseball that Donner has been carrying around.

It was a touching story of how it was Sharons baseball that she caught at a game just before the Mars Mission and she had taken it to Mars with her as a good luck charm. Since clearly it did not bring her any luck as she was abandoned on Mars, Donner took it upon himself to carry the burden of losing her and carried that baseball around everywhere he went - including on the Antares. It was a dual reminder of his lost love, and guilt he felt over leaving her behind. It was his burden and he could not just put it down. We saw how he tried to get rid of it by returning it to Sharons mother, but she then just mailed it back to him. She did not want that burden.

After 10 years of carrying it, Donner finally just threw it out into space. He was letting go of Sharon - setting her free. As Donner quietly shared, Letting go is the hard part because our past defines us ... but what we decide becomes a part of who we are. At the end of the episode, as the Antares crossed the Rubicon-point, Donner also noted, We may cross the river, but our footprints will always remain on the other side. It is not that he wants to forget Sharon, but it is time to let go and move on.

It was also about time that Eve (Karen LeBlanc) started wondering what had actually happened on Mars. Her confrontation of Goss (Andrew Airlie) after uncovering his lies about it was admirable. It would be even cooler if she was able to get him forced out after such a fatal dereliction of duty. It was because of his panic-attack that two people died.

Another cute aspect of the episode was discovering that Jen (Christina Cox) had not only kept one of the rabbit fetuses beyond the destruction date, but she had also named it Rufus and looked like she intended to keep it. When pushed by Rollie (Ty Olsson) about why she would want a rabbit on board, we began to see the softer-side of a person who now found herself alone and lonely. She wanted some companionship and to create a bunny rabbit seemed adorable.

Lastly, it was great to hear Ted finally ask Donner, Has it occurred to you that everything has gone wrong on this mission? To which surprisingly Donner answers, Maybe its us and Ted thoughtfully agrees, Maybe it is.

What Didn't Work

Is anyone else starting to wonder who the heck Jeff Walker is? He cannot just be the other astronaut left on Mars. Surely, there is a big piece of the backstory puzzle that his character is holding. I, for one, am dying to find out what it is. Lets hope it is not another loose end.

Giving Credit Where Credit Is Due

"Defying Gravity" stars Ron Livingston, Laura Harris, Christina Cox, Ty Olsson, Malik Yoba, Karen LeBlanc, Andrew Airlie, Maxim Roy, Paula Garces, Florentine Lahme, Zahf Paroo, Eyal Podell, Dylan Taylor, and Peter Howitt. "Rubicon" was written by Meredith Lavender and Marcie Ulin and directed by Fred Gerber.

Defying Gravity airs Sundays at 10 p.m. on ABC.