Your protagonist has green eyes in chapter two and grey ones in chapter nineteen. Her older brother becomes her younger brother somewhere in the second act. She grew up in Devon until a late revision moved her to Dublin, and nobody updated the scene where she talks about the sea.

That is not carelessness. It is what happens when a book is written over months, in scenes drafted out of order, with facts invented on the spot and quietly contradicted later. Consistency is not about freezing your characters. It is about keeping the promises you made to the reader — and that takes a system rather than a good memory.

Why Details Slip Between Drafts

Most inconsistencies come through one of three doors. You invent a detail mid-scene because the sentence needs it. You cut a scene that happened to establish something — a hometown, a dead father, a fear of water — and the fact disappears with it. Or you change a plot need late on, backfill the character to match, and forget what the earlier drafts already claimed.

None of these are failures of attention. They are what revision does. The answer is to treat character facts as data you keep somewhere other than your head.

Appearance: Six Details to Lock Down

Description drifts first, because it is the easiest thing to improvise and the easiest for a reader to catch. You do not need a police report. You need the handful of details you have actually given the reader, written down as you first wrote them.

• Eyes. Colour, and whether they wear glasses or contacts as a permanent feature or a one-off.
• Hair. Colour, length, texture, and any change the story itself causes. A haircut in chapter nine is a plot point; a haircut you forgot you wrote is a mistake.
• Build. Height, frame, and how they read beside other characters. If she has to look up at her brother, she looks up at him every time.
• Marks. Scars, tattoos, birthmarks — and precisely where. Which hand, which cheek, which wrist.
• Kit. The coat, the ring, the walking stick, the notebook. If an object matters once, decide whether it matters always.
• Physical habits. The limp, the slouch, the way they hold a cup, whether they smoke. Easy to drop, very noticeable when they return.

If a detail has never appeared on the page, you are free to change it. Once it has, it belongs in the file.

Voice: Track What They Would Never Say

Voice drift is subtler and harder to fix with a search function. It shows up as a character sounding like whoever else is in the scene, or like the narrator, or like the version of themselves you needed for one particular argument.

Four things are worth recording. How they build a sentence — clipped and blunt, or long and qualifying. The words they reach for: a doctor and a builder do not describe the same bruise the same way. The tics and catchphrases you have given them, and how often you have used them; one “right, then” is character, five is a tic. And what they never say — the subjects they steer away from, the apology they will not make, the form of address they refuse.

A character who says “I shan’t” in chapter one should not say “ain’t” in chapter ten unless something in the story has changed them.

Read the dialogue aloud, but read it in blocks: all of one character’s lines in a row. Drift that is invisible on the page is usually audible in the ear.

Backstory and Timeline: Check the Arithmetic

Timelines are where the sums go wrong. A character is thirty-two in a scene set in June and thirty-four by Christmas. Parents have their first child at nineteen and their second at forty-two without comment.

Keep a short timeline with dates and ages, even if none of it reaches the final book, then check the facts that carry weight: family structure, education and work history, and where the money comes from. Money is a consistency issue as much as a plotting one. A character who cannot afford a train ticket in act one needs a reason to be buying rounds in act three.

Skills work the same way. Someone who cannot swim in chapter four should not casually dive into a lake in chapter twenty unless they have been taught in between — and a single line is enough to make that credible.

Relationships: Names, Secrets and Shifting Ground

Relationships stay consistent when the small things do: what people call each other, how much they know, and where the balance of power sits between them.

Nicknames are a good test. If her sister calls her Beth at home and Elizabeth at the office, that contrast is doing work — so keep it steady and break it only on purpose. Then track knowledge. Who knows about the affair, the debt, the diagnosis, and when did they find out? Plenty of second-act confusion comes from a character reacting to news they were never told.

Allow relationships to change, though. Consistency does not mean a friendship frozen at chapter one. It means that when the friendship cools, the reader can see why.

The Fifteen Details Worth Tracking

Keep one page per main character, with a note of the chapter where each fact first appears so you can check it in seconds.

1. Eye colour, plus glasses or contacts.
2. Hair colour, length, texture, and any in-story change.
3. Height and build, relative to the other characters.
4. Scars, tattoos and birthmarks, with exact placement.
5. Signature clothing and carried objects.
6. Physical habits and mannerisms, including gait.
7. Vocabulary and register: the words they actually use.
8. Sentence length and rhythm.
9. Verbal tics and catchphrases, with a note on frequency.
10. What they never say, and which topics they avoid.
11. Age and birthday, against the story’s timeline.
12. Family: names, birth order, who is alive.
13. Education, work history and source of income.
14. What each character calls each other, and how that shifts.
15. Who knows which secret, and when they learned it.

Update the file as you write, not at the end. A fact you meant to record later is a fact you will have forgotten by the time later arrives.

The Single-Character Read

Once the structural edits are done, read the manuscript once per main character, skipping everything that is not theirs. It feels strange for the first twenty pages, then it becomes the fastest way to hear a voice go off-key.

Before that, run searches on the obvious words — eye colours, hair, ages, hometowns, the names of siblings. Fix what you find, and keep a short change log for the alterations you make on purpose, so a later edit does not quietly reverse them.

Change is allowed. Silence is not. If a fact moves, move it everywhere it appears, and your reader will follow you anywhere.

Photo: EsaRiutta / Pixabay