Mary Beth Talley was one of the graduate students trained by Dr. Charles Reid of the Progenitors. Fellow student Andrew Greene described her as a "Southern belle" who graduated summa cum laude from Duke University and already had five papers published by the time they began their program.
Mary Beth initially dated Andrew casually, then began dating Rob after he secured a special lab assignment. She reacted with distress when Rob disappeared, and when he appeared not to recognize her upon his return. It is not clear if she, like Andrew, realized that Rob had been replaced by a clone, but she became afraid of him after he began working full-time in Reid's lab. Near the end of his journals, Andrew seems to think that Mary Beth is beginning to flirt with Chain, a Research Associate in the Pharmacopeists.