What happens in Chapters 10 and 11 of The Egypt Game?

Ever since a little girl in the neighborhood is murdered and suspicion falls upon the Professor, the Egypt group has been kept under tight supervision and has been unable to return to their play area in the Professor's back yard.  The furor dies down by Halloween, however, and, led by April, the group is waiting for a sign that it is time to return to Egypt.  In Chapter 10, April, Melanie, Marshall, and Elizabeth go trick-or-treating with the children from Casa Rosada, but they are more interested in looking for their omen than getting candy from the neighbors.  They run into Ken Kamata and Toby Alvillar, "the most disgusting boys in the sixth grade", and while they are trading playful insults, Melanie spots a shooting star.  April says it is "the secret omen", and the four friends scurry away from the other children to go back to Egypt.  In the darkness of night, Egypt is especially fascinating.  April instigates "the Great Ceremony of the Celebration of the Return to Egypt, and the four prostrate themselves before the altars of Set and Isis (Chapter 10).

April says that the gods are angry that she and the others have been away for so long, and are demanding that they make a sacrifice of atonement, "a horrible and bloody sacrifice".  Elizabeth suggests that they should stick their fingers with a needle and write the gods a letter in their own blood, an idea she remembers from reading Tom Sawyer, but alas, the group has no needle.  April says that they should sacrifice something dear to them, like Security, but Marshall vehemently shouts his objectiion.  He says they should sacrifice April, and everyone laughts, even Marshall.  Melanie then comes up with the great idea of sacrificing some of their hair and nail clippings, and the group builds a small fire and does just that.  Suddenly Elizabeth and Melanie see "a huge misshapen figure teetering on the top of the high board fence".  The figure "teeter's) wildly in the dim light, and then (springs) forward to land in a horrible threatening crouch, right in the middle of Egypt" (Chapter 11).