Complex sentence: When the full moon rises, David painfully strips off his clothes and transforms into a werewolf and starts to prowl the streets and the London Underground, slaughtering six Londoners in the process.
Split into simpler sentences: When the full moon rises, David strips off his clothes and painfully transforms into a Werewolf. He then begins to prowl the streets and the London Underground, slaughtering six Londoners in the process.