Complex sentence: They return to Springwood and Mark abruptly tells Lori and the others about Freddy, then later realizes the city's plan of erasing Freddy by making the population forget about him and that he may have ruined their plan.
Split into simpler sentences: They return to Springwood and Mark abruptly tells Lori and the others about Freddy. He, later learn of the city's plan to erase Freddy by making the population forget about him and that they may have ruined their plan.