"Always two there are, the master and the apprentice."

When these words are uttered at the conclusion of The Phantom Menace, it is clear to viewers that Darth Sidious will be replacing his apprentice, Darth Maul.

However, the word "always" means there should be no break. Indeed, is it not true that at the moment this line is spoken, there is in fact only one Sith?

The Phantom Menace certainly seems to indicate that. After all, we've seen no new Sith apprentice emerge. However, a closer examination of dates says that Count Dooku might have assumed the mantle of Darth Tyranus very near to Maul's death.

We'll start by laying out the timeline. The Phantom Menace occurs in 32 B.B.Y.; Attack of the Clones occurs in 22 B.B.Y., ten years later. We know from Anakin's age (he's nine during TPM, but ten in the final scene, and twenty in AOTC) that we're actually working with one year and probably a couple months; it'd be like if TPM was in January of 1992 and AOTC in June of 2002.

Now, turning to the AOTC script, we have the following:

OBI-WAN: You mentioned growth acceleration...

LAMA SU: Oh yes, it's essential. Otherwise, a mature clone would take a lifetime to grow. Now, we can do it in half the time. Those items you saw on the parade ground were started ten years ago, when Sifo-Dyas first placed the order, and they're already mature.

So, the order for clones was placed by Sifo-Dyas ten years prior to AOTC--this would make it months at the most after TPM.

Also in the script, we have this:

OBI-WAN: Then you must know Master Sifo-Dyas?
...
JANGO FETT: Master who?

OBI-WAN: Sifo-Dyas. Is he not the Jedi who hired you for this job?

JANGO FETT: Never heard of him.

OBI-WAN: Really.

JANGO FETT: I was recruited by a man called Darth Tyranus on one of the moons of Bogden.

This is important: Dooku was going by the name of Tyranus when he recruited Jango. This means he had already become a Sith substantially prior to when the Kaminoans began the first batch of clones ten years prior--he had to have the time to recruit Jango Fett for the job.

We also know that Dooku left the Jedi Order around the time of the Battle of Naboo, and that the death of his former apprentice, Qui-Gon Jinn, proved to be the final straw for him. Since Dooku is the one who erased the records of Kamino in the Jedi Archives, he was in league with the Sith. Was he a Sith yet? Well, we know for certain that he was working with them shortly after TPM.

And now, the kicker:

LAMA SU: Jedi Master Sifo-Dyas. He's still a leading member
of the Jedi Council, is he not?

OBI-WAN: Master Sifo-Dyas was killed almost ten years ago.

Here, it seems, Obi-Wan is slightly off with his dates. Well, wouldn't be the first time ("I haven't got by the name of Obi-Wan since, oh, before you were born.").

In truth, Sifo-Dyas had to be killed a little over ten years ago, because he was not a "leading member of the Jedi Council" during TPM--though he was when he placed the order.

The reason this is important is because Labyrinth of Evil reveals that Count Dooku killed Sifo-Dyas as his final act of initiation into the Sith Order.

That's right--Dooku passed his final test to become the Sith Apprentice prior to Maul's death.

What does that mean for Darth Maul? That his mission to track down the Jedi on Tatooine was a fool's errand--how can one explain the Sith being revealed to the Jedi over such a small goal? Darth Maul was put into harm's way to make way for his replacement, the far more useful Darth Tyranus.

Palpatine needed Count Dooku to head up the Confederacy of Independent Systems--there was no way Darth Maul was up to that task. Indeed, it seems Maul's sole purpose was to announce to the galaxy that the Sith had returned.

And it makes perfect sense that Palpatine would choose a showy, highly skilled warrior covered in Sith tattoos to make this declaration--the Jedi would be looking for similar warrior-Sith and overlook him and his political mechanizations.

Darth Maul was replaced before he ever met Obi-Wan Kenobi in battle.