It may end up as 11 or 12 parts, not quite sure.
9 - Sunnydale, 2003 - The Dawn of Man
The portal drops them into a charnel house. Dead demons everywhere, the whole school's shaking. "How long?" shouts Kevin.
"Twenty seconds," yells Strutter. "Don't linger, the building's collapsing. Ten.. ."
The portal opens, rubble falls through. With it, unnoticed, goes Anya's body. The midgets and Kevin follow.
They land under a black monolith. Apes watch fearfully as Strutter consults the map. "Ten minutes."
"That's her," says Og, pointing at the body. "The demon."
"Dead demon," says Strutter. He kicks the corpse contemptuously before they leave.
The apes are sniffing the corpse, torn between fear and hunger, when the Supreme Being arrives.
Previous parts are here:
8 - Sunnydale, Alternative Timeline 1998
7 - The Titanic, 1912
6 - Tunguska, 1908
5 - China, 1900
4 - The Alamo, 1836
3 - Castiglione, 1796
2 - Cadiz, 1588
1 - Sherwood Forest, The Middle Ages