Count on a Cowboy (Harlequin American Romance: Rocky Mountain Twins)

WAITING...TO FALL IN LOVE 

Stepping onto her estranged father's Colorado ranch, Brooke Harper hopes to find the missing piece of the puzzle that's left a hole in her heart—her long-lost sister. But the Bucking Q Ranch is deserted...except for the tall and rugged cowboy, Trent Landry, who is taking care of the place while the owners are away. She's determined to wait until the family she's never met returns home... 

And Trent will keep an eye on the mysterious Brooke until he finds out if she is telling the truth about finding her sister. Spending time alone with her, watching her take to ranch life as if she's a natural, he realizes she is definitely not a threat—except maybe to his heart.