Forbidden (Diana Cosby) Books in Order

The Recommended Reading Order for the Forbidden Series

For readers looking to dive into Diana Cosby’s signature blend of Knights Templar mysteries and high-stakes medieval romance, the best path forward is to follow the publication order. Because the books follow a chronological progression starting shortly after the historical 1307 persecution of the Templars, reading them in sequence helps you appreciate the evolving political alliances and the larger mystery surrounding the Templar secrets.

Here is the recommended reading order for the Forbidden series:

1. Forbidden Legacy (2016) – Follows Sir Stephan MacQuistan and Lady Katherine Calbraith.
2. Forbidden Knight (2017) – Follows Sir Thomas MacKelloch and Mistress Alesone MacNiven.
3. Forbidden Vow (2018) – Follows Sir Aiden MacConnell and Lady Gwendolyn Murphy.
4. Forbidden Alliance (2019) – Follows Sir Cailin MacHugh and Elspet McReynolds.
5. Forbidden Realm (2020) – Follows Sir Rónán O’Connor and Lathir McConaghy.

Detailed Summary of the Forbidden Books

1. Forbidden Legacy (2016)

The series begins with Forbidden Legacy, which introduces Avalon Castle, a stronghold caught in the crossfire of the Scottish-English conflict. Lady Katherine Calbraith is determined to protect her birthright after her family is murdered by the English. She agrees to a marriage of convenience to the mysterious Sir Stephan MacQuistan. What Katherine does not know is that Stephan is a surviving Knight Templar who seeks Avalon Castle to store the order's treasures—and to seek vengeance against the family that stole his childhood legacy. As their marriage unfolds, their mutual mistrust gives way to a fierce, undeniable passion.

2. Forbidden Knight (2017)

In the second installment, the focus shifts to Sir Thomas MacKelloch, a Templar knight serving King Robert the Bruce. Near the King's camp, Thomas captures a suspected assassin, only to discover she is Alesone MacNiven, a skilled healer loyal to the Scottish crown. However, Alesone holds a dangerous secret: she is the daughter of Lord Comyn, the King’s mortal enemy. When the King orders Thomas to escort Alesone to safety to prevent a politically disastrous marriage, the two are forced to navigate the treacherous Highlands together while battling their past traumas and growing attraction.

3. Forbidden Vow (2018)

Forbidden Vow centers on Lady Gwendolyn Murphy, who is awaiting the arrival of her betrothed, Bróccín MacRaith. Upon his arrival at Latharn Castle, Gwendolyn finds herself drawn to the imposing warrior, unaware that the real Bróccín has died. The man posing as him is Sir Aiden MacConnell, a Templar knight who took the dead man's identity to gain access to the castle for his order's mission. As the wedding date approaches, Aiden must choose between his sacred duty and his love for the woman he is actively deceiving.

4. Forbidden Alliance (2019)

In the fourth novel, we meet Elspet McReynolds, who has been forced into a life of outlawry in the forests surrounding Tiran Castle after her family home was seized. She crosses paths with Sir Cailin MacHugh, a Templar knight and the true heir to the earldom of Dalkirk, who was long believed to have died at sea. Bound by a shared enemy and a desire for justice, Elspet and Cailin form a dangerous alliance to rescue her brother and reclaim Dalkirk, finding love along the way.

5. Forbidden Realm (2020)

The final book in the series, Forbidden Realm, takes the action across the Irish Sea. Sir Rónán O’Connor is an Irish-born Templar knight who has sworn never to return to his homeland. However, duty calls him back as he is tasked with transporting a critical cache of Templar armaments for King Robert the Bruce. Along the way, he must protect Lathir McConaghy, a fierce Irish warrior guarding her own heart after the loss of her fiancé. When a sea attack leaves them shipwrecked, they must rely on each other to survive the political turmoil of medieval Ireland.

What to Know Before You Start

Before launching into the Forbidden series, it helps to understand the historical context that drives the overarching plot. Diana Cosby set the series in the 14th century, operating under the historical premise that surviving Knights Templar fled to Scotland after the French King Philip IV ordered their arrest in 1307. In Cosby's universe, these knights use their military prowess to support Robert the Bruce in exchange for sanctuary and a place to secure their legendary treasures.

While the Templar backdrop and occasional recurring secondary characters provide continuity across the books, each romance resolves completely by the end of the novel. This means that if a particular trope or character catches your eye, you can technically read the books as standalones without feeling lost.

Connections to Other Diana Cosby Series

Diana Cosby is well known for her medieval Scottish romances, specifically her debut MacGruder Brothers series and The Oath trilogy. Readers often wonder if the Forbidden series connects to these other works. They are independent series set in the same general historical era, but they do not feature overlapping characters or spin-off plots. You do not need to read the MacGruder Brothers or The Oath to enjoy the Forbidden series, making the latter an excellent entry point for new readers.