Complex sentence: Tessa reminds Stefan that Silas knows where the anchor is due to this mind reading power and she has to kill him before he tries to destroy it but when she tries to get out of the cabin she can't because Silas cast a spell on it.
Split into simpler sentences: Tessa reminds Stefan that Silas knows where the anchor is due to his mind reading power so she has to kill him before he tries to destroy it. But when she tries to leave the cabin she can't because Silas cast a spell on it.