Complex sentence: Two of them are told they are survivors of a fatal airborne disease that is sweeping over the entire world; however, their induced isolation may be the result of a lie, and it may be that they are being held at the whim of a madman.
Split into simpler sentences: Two of them are told they are survivors of a fatal airborne disease that is sweeping over the entire world. However, their induced isolation may be the result of a lie, and it may be that they are being held at the whim of a madman.