Complex sentence: He goes to study the manuscripts from Merlin's cave, discover that Mitchell and Carter have been shifted much as he was-however, the device exists in both dimensions, so they begin to communicate by pressing buttons on the device.
Split into simpler sentences: He goes to study the manuscripts from Merlin's cave and discovers that Mitchell and Carter have been shifted much as he was. However, the device exists in both dimensions, so they begin to communicate by pressing buttons on the device.