[Steven Universe] Garnet isn't really Garnet

Warning, major spoilers for Steven Universe if you're not up to date yet!

Garnet is one of the heroes of the television show Steven Universe. She's the coolest space rock about and a firm friend and protector of Steven... or is she? Can we really be sure that Garnet is actually Garnet?

No. No we can't.

Season one was littered with lots of clues that Garnet was actually a fusion, two beings combined into one. This was confirmed in the season one finale 'Jailbreak'. Season two looks to be following a similar trail of earth-shattering clues about Garnet, namely that Garnet was replaced by a spy at the end of season one. There is plenty of evidence to suggest this is the case:

• At the end of 'The Return', we see that Garnet is poofed back to her gemstone state. This is the point that the switch took place. The Ruby and Sapphire we meet in Jailbreak are not the Ruby and Sapphire that make up Garnet, but evil Homeworld spies.
• We know from 'Reformed' that if a Gem reforms too quickly from their gemstone state they will come back with horrible mutations. This can take hours to weeks. Given how quickly the fleeing Beach City citizens return to the city once the giant space hand is destroyed and the fact that the giant space hand has only made it to low orbit by the time it is destroyed, we know that barely any time has passed. So how are Ruby and Sapphire fully formed without any horrible mutations? Because they were there all along!
• We know Ruby and Sapphire exist, as the other Gems are aware of them, but we don't know what they look like! This is a classic trick of misdirection. As Pearl and Amethyst speak about Ruby and Sapphire and we see Ruby and Sapphire, we assume they are the same characters. But how can we assume this?
• We briefly see the outlines of Ruby and Sapphire in Fusion Cuisine. But they look completely different, especially Ruby. Ruby has tiny little string arms waving above her head. Almost as if they are different Gems entirely! Which they are!

• Garnet is suspiciously reluctant to let Ruby and Sapphire out in front of Pearl and Amethyst, presumably as they would instantly recognise that they aren't the real Ruby and Sapphire. The only time we see these characters are in front of Steven (who has no idea what they are supposed to look like) and Greg (who clearly knows about them, but as a human would not necessarily pick up on any changes).
• The new Garnet looks different to the old one. Pearl and Amethyst have previously changed their outfits, but Garnet's change is far more dramatic, even down to hair size and skin tone. Almost like... she is a different Garnet!

• Clearly this was the plan all along. After all, the escape from the giant space hand was done with Jasper's help, the two taking part in a choreographed song and dance routine for Steven's benefit (who was watching this on a monitor from the control room).
• Why did the Gem Homeworld want to capture Steven only to let him go? As he has the power of Rose Quartz, a powerful Gem leader, they Diamond Authority clearly want to monitor him and presumably shape him to their will. This new Garnet is perfectly poised to do this.
• As leader of the group, Garnet is responsible for the continued failure of the Gems to capture Peridot, despite Peridot's escape attempts consisting of moving slowly away. Obviously as a Homeworld agent, Garnet is invested in Peridot's freedom.
• Likewise, Garnet is seen to be constantly searching for Malachite alone, and yet still hasn't found her. How convenient!

As can be seen, there is a lot of compelling evidence that Garnet was replaced by a Homeworld agent at the end of season one. What are her true plans towards Steven? Will he wake up one day to a gauntlet in the brain? Or is Yellow Diamond's plan even more sinister?