What is the source of tension in this excerpt?

Read the excerpt from "Object Lesson, Part 2."

Ellery searched everything in the room, from the socket of

the American flag to the insect-filled bowls of the old light

fixtures, reached by standing on desks.

Everything

"It's not here!" whispered Louise in his ear.

O Ellery searching everything

O insects filling the light fixtures

Ellery standing on the desks

Louise Carpenter whispering