Complex sentence: McMissile and Shiftwell invite Mater to join them in another spy mission, but he graciously turns it down but asks Shiftwell for a date when she returns which she accepts.
Split into simpler sentences: McMissile and Shiftwell arrive and invite Mater to join them in another spy mission, but he graciously turns it down. He does ask Shiftwell for a date when she returns which she accepts.