Possible Clues:

• Skeptic
• One may be troubled, somehow not trustful ultimately
• 'Not dinner, by the sound of it? Not sure (7)'
• Sceptic
• E.g. St Thomas
• A certain Thomas, say, as one performing, but troubled within
• One who is not sure
• Thomas was one man of action, but quaking on the inside
• Origins of British tank engine are in dreary one such as Thomas
• Thomas was determined to hide silly bet