A surprise party draws an A-list crowd on “Nashville” (9 p.m., ABC), including music stars Dan Auerbach (the Black Keys), Vince Gill, Pam Tillis, Kip Moore and Kate York.

To my mind, the best female singer on this great show isn’t Rayna (Connie Britton) or her bratty rival, Juliette (Hayden Panettiere), but the young Scarlett (Clare Bowen), whose duets with Gunnar (Sam Palladio) have been moving and memorable alternatives to the arena anthems of the show’s big stars.

Melodramas often create characters you love, or love to hate, but Scarlett brings out a protective instinct in her Uncle Deacon (Charles Esten) and her songwriting partner, Gunnar, as well as the audience. Viewers may be surprised that Scarlett, the naive and vulnerable Mississippi talent, is played by an Australian actress.

There’s no guarantee that “Nashville” will be renewed for a second season. But I’m pretty confident that Rayna and Juliette will be rivals again, with Britton and Panettiere vying for best actress honors at the Emmys. And if I had to choose, I’d opt for Panettiere. Juliette hasn’t always been likable, but she’s been intense and real, and above all, her character has grown.

Tonight’s other highlights:

• “American Idol” (7 p.m., Fox) trudges forward.

• Deadshot returns on “Arrow” (7 p.m., CW).

• A hip-hop star tries to beat a domestic violence rap on “Law & Order: Special Victims Unit” (8 p.m., NBC).

• Mitchell and Cam are best men in the worst way on “Modern Family” (8 p.m., ABC).

• Ivory poaching puts pachyderms in peril on “Battle for Elephants” (8 p.m., PBS).

• Careful viewers of the miniseries “Parade’s End” (8 p.m. and 9 p.m., HBO) will notice two “Boardwalk Empire” regulars, Stephen Graham and Jack Huston, in the cast.

• Killing more than time at the poker table on “CSI” (9 p.m., CBS).

• Treat Williams guest-stars as Severide’s father on “Chicago Fire” (9 p.m., NBC).

• An agent’s personal turmoil threatens the KGB’s Washington cell on “The Americans” (9 p.m., FX).

• “Duck Dynasty” (9 p.m., A&E) returns for a third season of contrived shenanigans.