Counterfeit Cowboy — Sharon Ervin

Jilted, Chelly Bennett, 25, believes her ex's charge that she “thinks too much.” Deciding she is too intellectual to fall in love--that she is a passionless woman whose brain runs the physical plant--Chelly runs to the city to hide in plain sight, and vows never to trust another man.
Despite her intentionally dowdy appearance, Chelly is hired as a clerk at Diet, Manning, Diet & Harned (DMD), an upscale law firm where she encounters Don, a handsome gofer whose G.Q. look is nullified by scruffy cowboy boots.
At DMD, Chelly quickly develops regard for D.R. Manning, the firm's perpetually absent partner whose primary contact with the office is by e-mail. Coworkers laud Manning's genius but describe him as crotchety, which Chelly mistakenly translates as old.
Chelly is totally captivated by both her cowboy and D.R. Manning before she discovers the truth: a deception that makes her ex's betrayal pale by comparison.