First look: Josh Charles on 'Masters of Sex'

Masters of Sex returns for a third season July 12 with a nearly five-year time jump, just as researchers William Masters and Virginia Johnson unveil their seminal book, and with a new complication.

Josh Charles, who played Will Gardner on CBS' The Good Wife, joins the acclaimed Showtime series (Sundays, 10 ET/PT) as Dan Logan, a fragrance-company executive who approaches Bill (Michael Sheen) and Virginia (Lizzy Caplan), wondering "if you can literally bottle the smell of sex," says creator Michelle Ashford. "If anybody can do it, it would be these people."

Like some of Sex, the biographical details are true: Logan is based on Hank Walter Jr., a former CEO of leading olfactory supplier International Flavors and Fragrances. And his presence proves pivotal: "This man came into their lives, and unwittingly becomes the catalyst for massive changes and upheavals," Caplan says.

Is there a new romance blooming? Says Ashford: "Things get really complicated, in a good way."

The new season opens in 1965, just as Masters and Johnson prepare to publish their first book, Human Sexual Response, the result of a decade's worth of laboratory work. "They're going from two people whose work only exists behind closed doors to celebrities, and that is going to bring a whole lot of changes," Caplan says.

For starters, "Bill is no longer her superior" — they are equals now — and Virginia "voices her opinion far more than in previous seasons," Caplan says.

Ashford promises a lighter tone than the second season, which saw the disintegration of "incredibly damaged" Masters' personal life, and ended with Johnson's custody battle for her kids (now played by new actors). "They both changed so significantly as a result of finding each other," and as the show progresses, Masters' "three-way marriage" to his wife Libby (Caitlin FitzGerald) and Johnson is "much more formal, and in a configuration they lived in for many years."

Charles, who appears in 10 of this season's 12 episodes, starting July 26, is best known for playing the law partner murdered in a courtroom in a shocking fifth-season twist of Good Wife. "We always had Josh at the top of our list" for the role, "just because he's incredibly charismatic and an intelligent actor," Ashford says. "We really wooed him."

Caplan says Charles, who declined an interview request, "fits in seamlessly" with the cast and "brings a completely new energy" to the series, joining returning guest stars Sarah Silverman, Allison Janney and Beau Bridges. "Josh is just a fun hang."