Marrying Mr. Gibson — Alina K. Field

She won't be forced into marriage to a nobleman's by-blow.

Paulette Heardwyn rushes to visit her dying guardian, set on learning the truth about her father and the treasure he supposedly left her. But the only man with answers takes his secrets to the grave, leaving her penniless--unless she marries his illegitimate son.
He won't be trapped into marriage by a father he's never known.

With Napoleon vanquished, an ex-soldier has plans for India. But before he can leave England, he's summoned to the deathbed of an Earl who's a spymaster, a complete stranger...and his father. And the meddlesome Earl expects him to marry the daughter of one of his spies.

Thrown together when an old enemy strikes, the would-be spouses soon realize: the Earl has set a trap that neither of them wants to resist.
PREVIOUSLY TITLED THE BASTARD'S IBERIAN BRIDE