Group Fifteen Files Books in Order

Where to Start with the Group Fifteen Files

The Group Fifteen Files is a series of fast-paced, high-concept spy novellas curated by thriller veteran Mark Dawson. Set in the same universe as his bestselling John Milton and Isabella Rose series, these compact books dive deep into the gritty, off-the-books operations of 'Group Fifteen'—a clandestine British black-ops division that handles tasks too dirty or legally impossible for MI5 and MI6.

For the best reading experience, we recommend following the publication order. Although some books serve as historical prequels, starting with the modern-era novellas establishes the ruthless nature of the agency and makes the Cold War-era origins feel far more rewarding. Reading them in this sequence also mirrors the way the series grew, introducing you to the overarching network of operatives, handlers, and the heavy moral conflicts that define their missions.

The Group Fifteen Files in Publication Order

1. Scorpion (2017) – Co-authored with Steve Cavanagh
2. Witness X (2017) – Co-authored with Scott Mariani
3. Little Sister (2018) – Co-authored with Michael Ridpath
4. The Vault (2020) – Written by Mark Dawson
5. Wormwood (2022) – Written by Mark Dawson

The Chronological Reading Order

If you are a timeline purist, you might prefer reading the series chronologically. The Group Fifteen Files spans decades, moving from Cold War Berlin and Soviet Russia to modern London and the Scottish Highlands. The chronological sequence rearranges the files based on when the core missions took place:

1. Wormwood (Starts in 1969) – Operative Eloise Shepherd's first attempt to exfiltrate a Soviet nuclear physicist begins here, before leaping forward to the Chernobyl disaster in 1986.
2. The Vault (Set in 1986) – Head of Berlin Station Harry Mackintosh recruits a professional cracksman for a high-stakes heist behind the Berlin Wall.
3. Scorpion (Modern Era) – John Milton is sent on a lethal assignment to eliminate an assassin targeting a journalist.
4. Witness X (Modern Era) – Disgraced agent Bryan Duffy is pulled back into active duty to neutralize a North Korean hit squad in London.
5. Little Sister (Modern Era) – Former SAS soldier Bjorn Thorsson must protect his sister from the very agency he once crossed.

Deep Dive: The Group Fifteen Files Book-by-Book

1. Scorpion (with Steve Cavanagh)

The series kicks off with a powerhouse collaboration between Mark Dawson and legal thriller maestro Steve Cavanagh. Scorpion places John Milton—Group Fifteen's deadliest asset, also known as 'Number One'—in the crosshairs of a moral dilemma. Dispatched to hunt down a lethal assassin who has targeted an investigative journalist, Milton must navigate a web of corruption while executing his mission with ruthless precision. Cavanagh's influence injects the narrative with relentless pacing and authentic procedural tension.

2. Witness X (with Scott Mariani)

For the second file, Dawson teamed up with Scott Mariani to introduce Bryan Duffy. Once a trusted agent, Duffy is now disgraced and living on the margins. However, when a cell of highly trained North Korean assassins begins targeting individuals in London, the agency realizes only Duffy has the specific skill set required to neutralize them. Witness X is a gritty, metropolitan thriller that explores the heavy cost of loyalty and the desperation of an operative with nothing left to lose.

3. Little Sister (with Michael Ridpath)

Co-authored with Michael Ridpath, Little Sister shifts focus to Bjorn Thorsson, a former SAS soldier trying to leave his violent past behind. When his sister inadvertently becomes a target of Group Fifteen's intricate political schemes, Bjorn is forced to stand against the very organization that rules the shadows. Set against the atmospheric backdrop of the Scottish Highlands, this novella highlights the terrifying reach of the agency when its secrets are threatened.

4. The Vault

Written solely by Mark Dawson, The Vault acts as a historical prequel set at the height of the Cold War in 1986. The story follows Harry Mackintosh, the veteran head of MI6's Berlin Station. Needing to crack a highly secure vault in East Berlin controlled by a ruthless Stasi general, Mackintosh recruits Jimmy Walker, a career criminal and expert cracksman. It is a classic, atmospheric heist story that reveals the early operational strategies that would eventually shape Group Fifteen.

5. Wormwood

The fifth installment, Wormwood, is a multi-timeline epic centering on Eloise Shepherd and the enigmatic British agent Vivian Bloom. The narrative begins in 1969 as Eloise attempts to smuggle nuclear physicist Stanislav Kalashnik out of Soviet Russia. When the operation ends in disaster, she is forced to wait 17 years for a second chance. Jumping to 1986 against the backdrop of the Chernobyl nuclear disaster, Eloise must venture back into Soviet territory for a desperate rescue. Wormwood adds massive lore to the origins of the agency and connects deeply to characters featured in the broader Isabella Rose series.

What to Know Before You Start

Before you dive in, there are a few practical tips to keep in mind. First, the Group Fifteen Files are designed as novellas, meaning they are much shorter and faster to read than Dawson's main John Milton novels. They are designed to be read in a single sitting, making them ideal for quick thriller fixes. Second, while these stories function perfectly as standalones, they heavily enrich the lore of the main series. Seeing John Milton during his active years in Scorpion or learning about handlers like Michael Pope and Vivian Bloom adds invaluable context to the wider 'Milton-verse'.