To Catch a Fortune — Rochelle Alers

The enemy next door…

Had a hold on his heart!  

Oil entrepreneur Jonathan Porter's jet-setting ways come screeching to a halt when he learns he's the father of an orphaned son he never knew about. As Jonathan settles into his new home in Emerald Ridge, Texas -- and figures out parenthood -- the Porter family prodigal comes straight into the crosshairs of Vivienne Fortune. The formidable ranch forewoman's used to playing tough to be taken seriously at managing her wealthy family's property. But as Viv realizes Jonathan's a welcome ally against the saboteur hell-bent on destroying her family, she also discovers that her handsome new enemy might be more lover than foe! 

From Harlequin Fortunes of Texas:

Book 1: Faking It with a Fortune by Michelle Major
Book 2: A Fortune's Redemption by Stella Bagwell
Book 3: A Fortune with Benefits by Jennifer Wilck
Book 4: Conveniently a Fortune by Michele Dunaway
Book 5: To Catch a Fortune by Rochelle Alers