There is a trial for the Royal Guard, whom everyone thinks killed the prince.

At this point, the Tiefling makes his first appearance, outright accusing OP of killing the prince. His justification? OP had hated them for being in love. Before that could get very far, the other party members pointed out that, on the surface, OP would not have a reason to kill the prince, because of his patriotism, had been friends with both lovers (he suspects that the DM was trying to get him into a threesome or in a relationship with another elf), and had a good alibi.

OP demands his rights as a diplomat (which his party are being treated as, although technically they weren't) to hold the guard, and keeps him in the cellar of the party's manor.

Here's how he held the Guard: First, OP blindfolded the prisoner and put his arms in an iron sleeve-like thing so that he couldn't get the blindfold off, and be able to use his power of teleportation (the Royal Guard was an Eladrin, which was a kind of elf that could teleport). He then constructed two Magic Circles against the Fey, one around the wall, and a secondary one in the room that the Guard was held in, as well as setting up an Eyes of Warning ritual (makes an almighty racket if someone considered an 'intruder' steps over a designated line) in case the Tiefling got any ideas about trying to free the prisoner.

This is before the trial, and the Guard could not be allowed to testify, as it was his word against a gardener's about the fight, and the Guard's word would probably be believed, because Twu Wuv.

The players are in the Elven Nation. Their job is to get the prince back to the Human Nation and stop the war. There's only one thing wrong. The war has been incredible for the human nation (because the DM wanted to show the humans being greedy jerks), revitalizing the economy, patriotism, and all other such things, and OP was a patriotic human, who also appeared to be taking notes from Light Yagami from Death Note.

So, this is how it went. The OP disguised himself and the Half-Orc as the prince and his elvish lover, and went walking in the garden while the real prince and his lover were elsewhere. They made sure to be in sight of a gardener, and then had an argument. Tears were shed, angry words spoken, and finally (with the gardener as witness), the "prince" struck the "elf" across the face.

The DM went with this mostly because OP told her that what he was doing was part of a complicated scheme to get the Prince home incognito.

Then, the big part of the plan. There was a party that night, and OP made sure that everyone thought he was passed out drunk (really it was his familiar, who he disguised to look like him), disguised himself as a servant, and brought wine mixed with sleeping potion. While they were both asleep, he created a phantom warrior (who could attack like a real one), and killed the Prince (possible because the Prince was level 1). He then soaked the prince's lover's sword in blood.

At that point, he returned to his room and drunk himself asleep (to fool lie detection spells; he could truthfully say that he'd drunk himself asleep that night, and have an alibi)

When we last left our heroes, they had taken charge of the Royal Guard and imprisoned him in the cellar of their manor. He is prevented from leaving the corner he's in by some Magic Circles against Fae, there's an Eye of Warning ritual in case the Tiefling tried shenanigans. The Guard himself was blindfolded and had his arms tied behind him in a sort of iron sleeve thingy, because his race (Eladrin- a close relative to elves) can teleport to anywhere they have line-of-sight to.

With that out of the way, here's what happened with the plot: The DM decided that the elvish investigators would question everyone on their alibis. OP's was that he had underestimated elvish wine and had been passed out drunk.

To foil Detect Lies spells, he told the truth: He had indeed drunk too much wine and passed out that night. He'd just done it after he'd killed the Prince (he failed to mention this bit).

The real fun happens when his compatriot, the Ranger, is questioned, and something comes up. In OP's words "I don't know whether it makes my compatriot brilliant, or intensely creepy". When the Ranger is questioned, she ends up admitting that she had slept with him while he was drunk. OOC he doesn't know quite what to think, as he knows she did it to secure her alibi.

Meanwhile, the Dwarf brothers spent their time messing with the elf casting Discern Lies. They did it like this: The Bard brother, who had high charisma (and thus Bluff) would tell an outrageous story and be believed, and then the Fighter, who had Charisma as his dump stat, would confirm it, which would show as a lie. Sometimes they'd switch off. Also, they wore identical clothing. Quoting OP: "Dwarves love to make Elves suffer."

The Tiefling did his best to cast suspicion on OP. He actually got caught out in several lies, claiming that OP had been "sneaking off".

The last party member didn't have much to say, had a solid alibi, and didn't know anything.

It wasn't a Parody Sue. The DM went and made a serious, very Sueish elven nation, and a player just decided not to go along with the DM's little sparkly railroad.