The Cost of Vices Review: Is It Worth Reading?

Verdict: A dark sapphic fantasy romance about two assassin exes trapped together on a job gone wrong — equal parts magic, vengeance, and combustible tension.

Best for: Readers who love enemies-to-lovers (or exes-to-lovers), morally grey heroines, magic systems, and second-chance sparks under fire.

Heat: 🌶️🌶️🌶️🌶️ (4/5 — charged, jealous, and steamy)

Rating: ★★★★ 4.18/5 average across 116 Goodreads ratings — a strong early signal for a new-series opener.

Tropes: Exes to lovers · Enemies to lovers · Second chance · Forced proximity · Assassins · Fantasy magic

Two assassins, one work contract neither wanted, and a whole lot of unfinished business — The Cost of Vices by Kestrel Martin opens the Costly Decisions series with magic, betrayal, and a pair of exes who can’t decide whether to kill each other or fall back into bed. If you’re curating the best dark sapphic romance books, this fantasy-flavored slow burn deserves a look.

What Is The Cost of Vices About?

The Cost of Vices follows Vesper, an assassin with formidable control over her Energy magic, a taste for pleasure, and a jealous ex she can’t seem to shake — largely because they’re trapped together in the same work contract. Vesper spends as much energy trying to escape the arrangement as she does completing her assignments.

Her ex, Bellamy, has a gambling problem that keeps landing her in trouble, and a stubborn belief that she can fix everything and win Vesper back — if a certain red-head keeps her hands to herself. Then one of their jobs goes catastrophically wrong, and the two find themselves on the run, marked for death by their own employer, forced to face old demons as dangerous secrets surface.

What Makes This Dark Sapphic Fantasy Work

Martin blends fantasy stakes with messy, magnetic romance. What stands out:

Two morally grey leads. Vesper and Bellamy are assassins with real flaws — jealousy, addiction, pride — which makes their pull toward each other feel dangerous rather than tidy.
Exes-to-lovers tension. The history between them is baked into every scene, so the forced proximity crackles from page one.
A genuine magic system. Vesper’s Energy magic gives the assassin premise a fantasy backbone rather than a generic backdrop.
High-stakes plot engine. A botched assignment and a death-marked contract keep the romance moving against a real ticking clock.
Slow-burn payoff. The infighting and reluctant reliance make the eventual reconciliation land harder.

Book Synopsis

Vesper is one of the best in the business — deadly, controlled, and perpetually irritated that her employer has chained her to a contract alongside Bellamy, the ex she can’t quite quit. She wants out. Bellamy, drowning in gambling debt and convinced she can still win Vesper back, wants the opposite: to keep her close and keep any rivals at bay.

When an assignment goes horribly wrong, the uneasy arrangement shatters. Suddenly the two are on the run, hunted by the very people who hired them, hiding out while trying to untangle the disaster their lives have become. As dangerous secrets come to light, they’ll have to decide whether their history is worth salvaging — or whether their constant infighting will get them both killed.

My Review

I’m a sucker for an exes-to-lovers setup, and The Cost of Vices leans all the way into the good parts of that trope. Vesper and Bellamy have the kind of history that makes every glance loaded, and Martin doesn’t rush to smooth it over — the jealousy and resentment are real, which is exactly why the sparks feel earned. Pairing that with a fantasy assassin premise and an Energy magic system gives the book a genre-blend I don’t see enough of in sapphic romance.

Vesper is the standout — competent, sardonic, and just self-destructive enough to be interesting. Bellamy is messier, and your mileage will vary on how sympathetic her gambling-and-possessiveness combo reads, but she works as a foil precisely because she’s not an easy person to root for. The “on the run, marked for death” turn injects genuine momentum, and the secrets that surface in the back half give both women something to reckon with beyond their romantic baggage.

Honestly, it’s not flawless. As a series opener it spends real estate on setup, and the constant infighting occasionally tips from tense into exhausting depending on your taste. A few readers will want the world-building spelled out more. But if you like your sapphic fantasy dark, prickly, and populated by women who make costly decisions, this is a propulsive, promising start that left me wanting the next installment.

Element	In The Cost of Vices
Central relationship	Vesper & Bellamy — assassin exes forced back together
Core tropes	Exes to lovers, enemies to lovers, second chance, forced proximity
Setting	A fantasy world of Energy magic, assassins & deadly contracts
Heat level	🌶️🌶️🌶️🌶️ (4/5)
Series	Costly Decisions Book 1
Content notes	Violence, assassins, gambling addiction, dark themes — check the author’s notes for the full list

How Spicy Is The Cost of Vices?

This one runs hot — around a 4 out of 5. Vesper’s appetite and Bellamy’s jealousy fuel a lot of the tension, and the exes-with-history dynamic means the intimate scenes carry emotional weight as well as heat.

It leans charged and sensual rather than purely explicit, with the friction between the two women doing much of the work. If you want spice woven into a real fantasy plot, this delivers.

Who Should Read This Book?

You’ll likely love it if: you enjoy sapphic fantasy romance, morally grey assassin heroines, exes-to-lovers tension, and magic systems layered under the swoon.

You may want to skip it if: you dislike heavy infighting, prefer a clean single-book resolution, or want dark themes kept off the page.

In short: a magic-laced, prickly, high-tension opener for readers who like their sapphic romance dangerous and their heroines flawed.

Frequently Asked Questions

Is The Cost of Vices a standalone?

No. It’s the first book in the Costly Decisions series, so it opens threads that continue into later installments, though it delivers a substantial arc of its own.

Is The Cost of Vices a true sapphic romance?

Yes. It’s a fully sapphic romance centered on two women — Vesper and Bellamy — navigating their fraught history as exes and assassins.

How steamy is The Cost of Vices really?

Quite steamy — roughly a 4 out of 5. The heat is amplified by jealousy, history, and the charged exes-to-lovers dynamic.

Does The Cost of Vices have a happy ending?

As a series opener it resolves major beats while leaving the larger story — and some relationship threads — open for the next book. Expect momentum toward a HEA rather than a fully sealed one here.

Do I need to know the magic system before reading?

No. The Energy magic is introduced within the story, so no prior knowledge is needed — this is the entry point to the world.

If You Loved The Cost of Vices, Read These Next

If the assassin magic, exes-to-lovers heat, and morally grey leads worked for you, you’ll find more to sink into in our roundup of the best dark sapphic romance books — from mafia obsession to fantasy-tinged enemies-to-lovers.

The Bottom Line

The Cost of Vices is a dark, magic-laced sapphic fantasy romance that pairs two flawed assassin exes with a death-marked contract and a slow-burning second chance. It’s setup-heavy and its leads are deliberately prickly, but Kestrel Martin builds a compelling world and a combustible dynamic that make this a strong start to the Costly Decisions series.

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