Complex sentence: But they appear to be out of the house when the Animorphs arrive, in fact Tom's Yeerk has already had Jake's parents infested and they spring a trap for the waiting Animorphs.
Split into simpler sentences: But they appear to be out of the house when the Animorphs arrive. In fact, Tom's Yeerk has already had Jake's parents infested, and they spring a trap for the waiting Animorphs.