Mummies in the Morning by Mary Pope Osborne

Jack and Annie wanted to explore the pyramid after finding the mummie's book and explored it. They got too lost to get out. So then went to their treehouse to go back home. So they got in the treehouse and found a letter on the floor of the treehouse. Then they were climbing down the ladder and heard a noise coming from the bushes and Jack thought it was M and they were cheering to find out who M is.