When one door closes, another opens. 

That common saying seems to be the recurring theme of The 100 Season 4 (so far), as Clarke and her people fight to save humanity from the oncoming deadly waves of radiation.

The 100 Season 4 Episode 3 illustrated this point perfectly, juxtaposing a massive failure with the discovery of a new possible saving grace.

Like The 100 Season 4 Episode 2, the action was once again split between Polis and Arkadia. Unlike "Heavy Lies the Crown," the split was more uneven – the Arkadia-centric bits got more attention, though Octavia and Indra's storyline in Polis provided some excellent character-deepening material.

The big news out of the Grounder capital? The flame (aka Becca Pramheda's ALIE 2.0, aka the "Spirit of the Commander") went missing. Roan was quick to point the finger at who robbed him – Gaia, the young woman we briefly glimpsed on The 100 Season 4 Premiere.

Initially, it's unclear why Indra has a look of barely-restrained panic on her face when Roan conscripts Octavia (by now, after her assassination of Rafael, a known up-and-comer in the bounty-hunter-for-hire world) to track down Gaia.

By the hour's end, the cause is revealed – the new flamekeeper is Indra's estranged daughter.

Heda would be ashamed.

Gaia [to Indra]

• Permalink: Heda would be ashamed.

Now, I'm not saying that the actual plot developments of this Polis storyline are unimportant. Obviously, they are – Octavia allowed Gaia to escape with the real flame, tricking the others into believing that they've successfully destroyed the commander's spirit. That's a significant development.

Octavia has chosen a side – and she's chosen against Roan and the faction of other grounders (including Ilian) who want to destroy all technology in order to ensure that not ALIE/chipped scenario ever happens again.

That will obviously cause friction if (when) King Roan discovers the truth. In all likelihood, this decision will only hasten the inevitable rift between Roan and the Sky People. I have no doubt in my mind that Echo will be able to convince Roan of Skaikru's treachery, especially once this flame business is revealed.

Also, secondary but still important – if (when) Clarke hears (incorrectly) that the flame was destroyed, she's going to lose it.

That flame was her last piece of Lexa. Thinking it destroyed (even though it's no longer in her possession) will completely crush Clarke. Hopefully, she finds out soon enough that Octavia actually protected the flame and gave it to Gaia.

So, yes, all of that will be important for the rest of the season to come. However, I was more moved by Indra's relationship with her daughter, and what it meant for her relationship with Octavia.

Looks like you found that daughter now.

Gaia [about Octavia]

• Permalink: Looks like you found that daughter now.

Ever since they first met, Indra and Octavia have had one of the most intense and interesting relationships on the show. By now, four seasons in, there's no doubt about it – Octavia is like Indra's surrogate daughter. Octavia, trained and molded by Indra (as Roan correctly pointed out), is the daughter that Gaia never was.

Gaia's dedication to the sacred flame and her decision to follow her flamekeeper "calling" was obviously something that Indra could never possibly understand. Indra is Trikru, through and through – a warrior.

"Losing" her daughter when she and Gaia parted ways (for Gaia to become a scout for the flamekeeper, searching the land for nightbloods) explains so much about Indra's tough exterior – she'd hardened herself and was hesitant to open herself up to anyone else.

The scenes in Titus' dungeon were thrilling, emotional, and simply stunning all around.

I was sure that Gaia would die. It just seemed like something this show would do, immediately following her reunion with Indra. Beyond thrilled that she didn't.

Meanwhile, major developments happened over in Arkadia. The most important of them was Raven's discovery that they have two months – not six – to come up with an apocalypse-proofing solution.

Abby had previously returned to Skaikru's home base after realizing that there was nothing useful she, a doctor, could do in Polis. There, she reunited with Clarke, but her attention was soon consumed with another, immediate issue: Luna and her grounders.

The oil-rig dwelling group had tragically been wiped out by the first waves of radiation. Living on the ocean and eating the irradiated fish (which soon enough started dying themselves) left them all suffering from what Abby called Acute Radiation Sickness (ARS).

In the end, only Luna, her surrogate "daughter," and a few others were still hanging on (by a thread). Accompanied by Nyko, they made their way to Arkadia for help, and en route, 40 more of them died. Yikes.

As an aside, isn't it hilarious how the majority of the grounders claim to loathe and distrust Skaikru. And yet, as soon as there's a legit medical emergency, many of them run there straight away? Classic grounders.

Skaikru at Arkadia dealt with two concurrent moral dilemmas this time around (SO MANY moral dilemmas, all the time, always). The first arose when Jaha presented a possible solution to the problem of housing so many people in a radiation-safe shelter.

What if I told you there might be a fallout shelter less than a day's drive from here? A fallout shelter built to sustain thousands.

Jaha

• Permalink: What if I told you there might be a fallout shelter less than a day's drive from here? A...

When Jaha told his tale of the "Four Horsemen" cult, it immediately seemed fishy. Because cults are, y'know – fishy. But on top of that, think about Jaha's history with chasing rainbows.

His first foray into finding "salvation" (the City of Light) inadvertently unleashed ALIE upon the world. His second – this Four Horsemen cult – was also a bust, albeit a (seemingly) less nefarious one. 

Did anyone really think that Jaha would lead Bellamy and Clarke to a massive radiation-proof bunker – only three installments into the 13-episode season? Yeah, I thought not.

But I can't fault Jaha too much for his wasting of Raven's van (needed for renovations) for a day.

His fool's journey (and the eventual discovery of the Four Horsemen members long dead in the pissed-off-graffiti-covered fallout shelter) led to some phenomenal character moments between him, Bellamy, and Clarke. 

It also appears that Jaha is the OG Bellarke 'shipper on this show.

In that sense, "The Four Horsemen" was quite similar to one of the show's strongest hours to date, The 100 Season 1 Episode 8.

While Clarke, Bellamy, and Jaha were off on their, unfortunately, time-wasting quest, back in Arkadia, Raven was getting a feel for being a leader who makes tough decisions.

In an excellent scene between Abby and Raven, Raven refused to hand over medication that could potentially save Luna's little grounder girl, Adria. Abby accused Raven of condemning Adria to death in an emotional and tense moment.

In the end, unfortunately for the little girl, it didn't matter either way. Murphy stepped up to steal the medication to give to Abby, but it didn't work on Adria. She (and the other grounders in Arkadia, save Luna) died from the radiation.

Lindsey Morgan gave a stunning performance as Raven struggled with prioritizing the future needs of the many over the present needs of the few.

She's trying to be pragmatic and realistic, but it's clear that she's not emotionless. Her reaction when Adria died proved that well. I continue to be thrilled that Raven is being given such a central, meaty role this season.

After Clarke's failure to secure shelter, she finally sat down to create the list of the 100 people who would be allowed to live in the fortified Alpha station. In a major moment, she added Bellamy's name as the 99th, before Bellamy walked up and added Clarke's when she couldn't bring herself to do it.

Commence emotional shoulder touching.

Obviously, this was a profound moment for their relationship. Bellamy has faith in Clarke, and in Clarke's leadership abilities, even when she doesn't have it in herself.

But amidst all the emotions and the darkness, there's at last, one small glimmer of hope.

Luna miraculously survived and began to self-heal from her radiation poisoning. Abby (hopefully correctly) deduced that it was Luna's nightblood giving her protections from ARS.

Based on the origin of the nightblood – it was created by Becca so she could handle the radiation on earth and from ALIE 2.0 – this makes perfect sense. But will creating a vaccine or radiation cure from Luna's blood be that straightforward? Doubtful.

Stray Thoughts:

• Not to be repetitive, but that Bellamy/Clarke hand on the shoulder moment really got me. I'm aware that there are far more dire things going on, but what can I say? I love their friendship/possible romance.

• Adina Porter is such a talent. Those scenes with Indra and Gaia broke me a little. But those of us who also watched American Horror Story Season 6 were already well aware of that. 

• I hope we see Gaia again. I'm sure we will.

• I want Nyko just to stick around. I've enjoyed his character ever since he was first introduced as Lincoln's ally. Let's keep him! Also, are he and Luna like a thing now? I could dig that.

• Let's just say I was more than okay with the lack of Jasper in this installment. I need a break from him.

• Emori is still dealing with Murphy's closeness with Ontari while he was in Polis last season. I don't particularly understand why the show is refusing this to contextualize the Murphy/Ontari encounter for what it was – a rape – but OK, whatever. We're now being told Murphy enjoyed it, so fine.

• "You jealous, Miller? Don't worry, there's enough of me to go around." God, Murphy, I love you so.

• "What are the things that eat the bugs and fish going to eat now?" WHAT INDEED, BELLAMY.

What did you think of "The Four Horsemen"? Share your thoughts by leaving a comment below and remember that you can watch The 100 online here at TV Fanatic anytime!

Caralynn Lippo is a staff writer for TV Fanatic. Follow her on Twitter.