Complex sentence: One Czarnian was off-world when he unleashed his plague, and by coincidence it happened to be his fourth grade teacher, Miss Tribb, who he happens to be under contract to deliver alive to his employer Vril Dox.
Split into simpler sentences: One Czarnian was off-world when he unleashed his plague, and by coincidence it happened to be his fourth grade teacher, Miss Tribb. Who he happens to be under contract to deliver alive to his employer Vril Dox.