The Secret Heart by Mary Lancaster

Betrayal, temptation and an impossible love.

Some suspect that Lily Villin is the true heart of the Hart Inn, a lucky house where love always seems to blossom, whatever the obstacles. But Lily has another secret. She is in love with an enigmatic nobleman, and no luck in the world can make such a marriage possible.
Randolph, Lord Torbridge, is a man of many secrets, in pursuit of a well-born traitor. But his visits to the Hart have increasingly less to do with his vital work than with the innkeeper’s beautiful daughter – until he discovers her gift for mimicry and enrolls her in a dangerous masquerade to unmask the enemy.
Being with her brings temptations he struggles to resist, for he will not ruin her and he cannot marry so far beneath his rank.
For once, it is not Lily’s talents but his own which are needed for this love to blossom – along with a little luck and ingenuity.