Possible Clues:

• Catherine ___ Jones
• Letter between epsilon and eta
• Greek 'Z'
• Greek letter that would be last in English
• Letter from abroad's unknown arrival time
• Welsh actress, Catherine __-Jones, b. 1969
• It follows epsilon
• Found written inside maze, Talmudic Greek character
• Riemann ___ function (mathematics concept)
• Greek character confined to maze, taurine