The season 5 premiere of Agents of S.H.I.E.L.D. kicked off with a fascinating twist. The team had expected to be arrested, but what they hadn't expected was to be brought before a Kree Monolith. They emerged from the Monolith in a desperate near-future nightmare, stranded in an airtight bunker that holds the last survivors of humanity. There's only one way home: the same way they got there in the first place. But if S.H.I.E.L.D. is going to achieve this, they first need to unravel the mysteries of the Kree Monoliths themselves.

How Do The Kree Monoliths Work?

We were first introduced to a Kree Monolith back in Agents of S.H.I.E.L.D. season 3. This ancient Monolith had been used to trap the monstrous Inhuman Hive on the distant world of Maveth. Over the centuries, it became the center of the cult that evolved into Hydra. Hydra regularly used the Monolith to transport sacrifices to Maveth, men and women who would act as Hive's host and preserve his life.

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On our side, a Monolith is a solid block that appears to be made of stone. It periodically dissolves into a liquid form, sweeping out and grabbing matter around it. If you're drawn into the wormhole, you're then transported to what seems to be a fixed point in spacetime. So far, we've seen both black and white Monoliths. It's tempting to assume that white Monoliths transport you through time, and black Monoliths through space. That said, time and space are linked, and it makes sense that wormholes would involve temporal as well as spatial displacement. The black Monolith transported Simmons to the deserted world of Maveth, and it's impossible to know where or not she actually traveled in time as well.

Here's where things get interesting. In most science-fiction shows, you create a wormhole by having two equivalent items at either end of the journey. That's the case in Stargate, for example, where you can only create wormholes between two Stargates. Agents of S.H.I.E.L.D. has taken a very different approach. Here, it is the Monolith that creates the wormholes, to a destination in spacetime that's fixed through unknown means.

As we saw in "Maveth," the problem is that planets are continuing to orbit at different rates. Simmons had to work out where the Monolith's wormhole would open next, and get there in time to jump through it.

How Can The S.H.I.E.L.D. Team Get Home Again?

So far, the Monoliths are unique in the wider MCU. They are the only things that can create portals through time and space. It's likely the Time Stone can allow time travel, and we know that the Space Stone can open portals across galactic distances. We can assume Infinity Stones are off the table for the S.H.I.E.L.D. team, so the Monoliths are clearly their only way home.

In this case though, it's going to be far more difficult. The Earth has been destroyed, and there's only one small inhabitable space station. The odds of the wormhole emerging in that space station's atmosphere anytime soon are pretty slim. What's more, it seems that the space station is moving at a faster rate than a planet would. That's why the S.H.I.E.L.D. team were scattered across the station, rather than emerging stood next to one another in the same room. So even if the wormhole does pass through the space station again, it may be very difficult indeed to get into it.

It's more likely that, in the end, Agents of S.H.I.E.L.D. will have to take a very different approach. They'll have a far better chance of getting back home if they can plot the wormhole's path through the Earth's debris field. It would then be a matter of matching the wormhole's speed, and conducting a hasty spacewalk into it. They'd then return to their own time.

None of this is going to be simple. Fortunately, Simmons already has a history of working with Monoliths, having calculated how these portals work on distant Maveth. Less fortunately, this time round the situation is far more complex. It's going to take all her genius to work this out.

Next: Could Agents of SHIELD Do Secret Invasion?

Season 5 of Agents of S.H.I.E.L.D. airs Fridays @ 9pm EST on ABC.