Complex sentence: Mrs Coulter has drugged her daughter Lyra and keeps her in a remote cave hidden from the Magisterium, a theocratic authority who are determined to kill Lyra to prevent her from becoming the second Eve and causing a new fall of man.
Split into simpler sentences: Mrs Coulter has drugged her daughter Lyra and keeps her in a remote cave hidden from the Magisterium, a theocratic authority. The Magisterium are determined to kill Lyra to prevent her from becoming the second Eve and causing a new fall of man.