Possible Clues:

• Brit's oath
• "Gosh," in Britain (hidden in RIGOROUS)
• 'Gosh,' in Britain (hidden in RIGOROUS)
• "Tarnsman of ___" (sci-fi book that launched an ongoing series)
• 'Tarnsman of ___' (sci-fi book that launched an ongoing series)
• Noted science-fiction universe
• Brit's exclamation