caught between Scylla and Charybdis

Caught between Scylla and Charybdis is an idiom which comes from Greek Mythology and is relative to the phrases between a rock and a hard place and between the devil and the deep blue sea. It is simply another way to say that you are stuck between two very difficult choices and have to choose between two evils. Scylla and Charybdis were both evil in Greek mythology, so being stuck between them means each choice is difficult.