We have to stop them getting any further into the school, Esther said.

Your sonar shield! Oliver said, remembering the pulse Esther had used in switchit practice.

A look of determination suddenly came over Esthers face. She changed her stance so that she was rooted to the ground, then pushed her powers outward. Suddenly, it was as if a shield had been placed around them, like a protective glass cloak.

The bats pelted the protective shield, screeching, flapping their horrible black wings. But they failed to penetrate the protective barrier, slamming instead against it.

Esther pushed the protective shield outward. It ebbed out like ripples on water, driving the bats backward.

Olivers mouth gaped open. Esther used her powers with such beautiful precision it made his heart hammer.

Youre amazing, Oliver stammered.

Thanks, Esther said through gritted teeth. But I cant hold this forever. We need to warn the others. Theres a panic button.

The strain was evident on her face. Oliver leapt to attention.

Wheres the button? Oliver asked.

With her full concentration on the shield, Esther called over her shoulder, There, in the trees!

Oliver turned and hurried for the large oak. When he reached it, he searched the bark, frantically trying to find anything that resembled a button. He noticed a raised knot in the bark, too perfectly spherical to be natural. Whispering a silent prayer beneath his breath, Oliver slammed his palm against the knot. Immediately, a shrill wailing sound pierced the air.

In just a matter of seconds, the once tranquil gardens were swarmed with teachers and security staff. Oliver saw Doctor Ziblatt amongst them, and Coach Finkle. There were also many guards, the Seers who dedicated themselves to defending the school.

Professor Amethyst emerged from the crowd. Esther. Oliver. Get back. Leave this to us.

Esther didnt need telling twice. She let her shield down and slumped forward with exhaustion. Oliver caught her in his arms.

Esther! he exclaimed, alarmed.

Shell be okay, Professor Amethyst assured Oliver. Shes just drained herself by using up all her powers. Just get her to safety.

Oliver nodded with determination. He slung Esthers arm around his shoulder and heaved her up to standing. She had just enough strength left to support her weight, but she leaned heavily against him as they hurried through the grass and along the path.

When they reached the open door to the gardens, Oliver saw yet more guards holding back crowds of students craning their necks to see what was going on.

Oliver took a quick glance over his shoulder. Immediately, he wished he had not. An epic battle was taking place in the once beautiful gardens. The bats were transforming into humans. Their eyes flashed blue.