Winter Longing by Rebecca Ruger

Firefighter and professional lacrosse player, Cole Carter, finds himself fantastically thrust back in time to 1303 Scotland. Struggling to adapt to the perilous medieval world, Cole faces suspicion and hostility from the fierce Highland clan with whom he finds shelter from the harsh winter.
Ailsa Sinclair, a sheltered young woman under the strict protection of her brother, Laird Tavis Sinclair, is at first wary and soon intrigued by Cole’s tales of the future. Against her brother’s wishes, Ailsa secretly helps Cole navigate his new reality, teaching him the ways of 14th century Scotland while finding herself drawn to this mysterious stranger.
As Cole and Ailsa’s bond deepens, so does the enmity of Tavis, who sees Cole as a threat to both his clan and his sister’s safety. Their forbidden romance blossoms amidst rising tensions, until a traitor reveals Cole’s origins at the same time the clan faces an imminent threat from an invading force.