The Investigator

Turn observation into a weapon. Let your enemies discover that you have already worked out their next move.

Every confrontation leaves clues. A shifted stance betrays an impending strike. A glance reveals a concealed accomplice. Mud on a boot tells you where someone has been, while the smallest hesitation exposes what they fear.

An Investigator sees the pattern and acts. You uncover secrets, read people, and enter combat with a plan already taking shape. A blade is dangerous in your hands because you know exactly where it needs to go. Your mind becomes your greatest defence, anticipating danger and finding a way through seemingly impossible challenges.

Your study extends to wizardry. Your spellbook is a working journal of arcane formulae, experiments, and discoveries, giving you the tools to expose deception, cross an obstacle, or spring a contingency at the perfect moment.

As your deductions sharpen, an opponent’s smallest mistake can unravel their entire approach. At the height of your ability, you can seize a decisive moment and make events unfold exactly as you anticipated.

Level 3: Spellcasting

Knowledge Is Power.

Your pursuit of answers has led you into the study of wizardry. You gain a spellbook and cast spells as a Wizard of one-third your Fighter level, rounded down, using Intelligence as your spellcasting ability.

You begin with three Wizard cantrips and six level 1 Wizard spells of your choice in your spellbook, just like a level 1 Wizard.

Every three Fighter levels thereafter (6, 9, 12, 15, and 18), you add two Wizard spells to your spellbook for free. Each must be of a level you can cast through this subclass.

Your effective Wizard level determines your spell slots, prepared spells, and further cantrip progression. You have access to the full Wizard spell list and can copy additional spells into your book and cast Rituals as a Wizard does.

This feature grants Wizard spellcasting only, not other Wizard class or subclass features.

Level 3: An Eye for Detail

You notice the misplaced object, the rehearsed answer, and the expression that disappears a moment too late. You gain Expertise in Investigation and Insight, gaining proficiency in either skill if you lack it.

Spellbook

Your spellbook is a working journal of arcane formulae, deductions, and discoveries. It begins with six level 1 Wizard spells of your choice.

At Fighter levels 6, 9, 12, 15, and 18, add two Wizard spells to your book for free. Each must be of a level you can cast through Knowledge Is Power. You can copy additional spells into your book as a Wizard does.

You prepare spells from those recorded in your spellbook, using your effective Wizard level to determine how many you can prepare. Your cantrips are known separately and do not occupy pages in your book.

Level 7: Careful Calculation

You use the power of your mind to overcome any challenge, anticipating danger, finding openings, and resisting threats through sheer mental discipline.

While you aren’t Incapacitated, add your Intelligence modifier to your Armour Class, attack rolls, damage rolls, and saving throws, in addition to their normal modifiers.

Apply the damage bonus once to each creature damaged by an attack or spell.

 

Level 10: Always Prepared

 

What appears to be an improvised response is often a contingency you worked out hours earlier.

When you cast a spell with a casting time of one Action, you can cast it as a Bonus Action instead. That casting also benefits from Subtle Spell, requiring no Verbal or Somatic components, nor Material components unless they have a specified cost or are consumed.

You can use this feature a number of times equal to your Proficiency Bonus, regaining all expended uses after a Long Rest.

The spell otherwise follows its normal rules, including spell slot expenditure and Concentration.

Level 15: A Predictable Mistake

 

You recognise the flaw in an opponent’s approach and manoeuvre them into a succession of mistakes.

As a Bonus Action, choose one creature you can see within 60 feet. It has Disadvantage on all attack rolls, ability checks, and saving throws until the start of your next turn.

You can use this feature a number of times equal to your Proficiency Bonus, regaining all expended uses after a Long Rest.

Level 18: The Final Deduction

 

Your deductions leave nothing to chance. At the decisive moment, events unfold exactly as you anticipated.

When you or a creature you can see within 60 feet makes a d20 roll, you can replace the result with a 1 or a 20. You can do so after seeing the roll, including after its outcome has been resolved. The replacement counts as the number rolled on the die, and the outcome is adjusted accordingly.

Once you use this feature, you can’t use it again until you finish a Short or Long Rest.

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Using the Spellbook on D&D Beyond

This subclass uses a repeatable spell register in place of the native Wizard spellbook panel. Each character has their own book; another player does not inherit anyone else’s spell selections.

Open your book

In the character builder, go to Class → Class Features → Spellbook. Use these choices to record the Wizard spells you have learned or copied. Learn your cantrips separately under the Spells tab.

Adjust the list length

Add: choose a spell from an empty Choose a Spell dropdown. The spell is saved as an entry and another empty field remains available, so the register can grow as you learn more spells.

Remove: open a saved spell’s dropdown and select Choose a Spell at the top. That entry is removed and the list becomes shorter. Clearing an entry is for correcting or removing a record; it does not grant a free replacement spell.

The register’s length is controlled by the entries you add or clear. There is no separate number box or slider. Three empty add-spell fields remain, one for each spell level this subclass can eventually cast. The displayed “Choices” total includes those empty fields; it is not your allowance of learned or prepared spells. Collapse the Spellbook section when you want a shorter builder view.

Record only spells you have learned

Your book starts with six level 1 Wizard spells. Add two more spells at Fighter levels 6, 9, 12, 15, and 18. You may also record additional spells you have copied using the Wizard’s normal copying rules. An unlimited register does not grant unlimited free spells.

Use the level 1 field from Fighter level 3, the level 2 field from Fighter level 9, and the level 3 field from Fighter level 15. D&D Beyond may display higher-level fields early; leave them empty until you qualify. Do not record cantrips in these fields.

Prepare and cast separately

Under Class → Spells → Add Spells, prepare only spells recorded in your book, up to the allowance below. When changing preparation after a Long Rest, unprepare the old choices and prepare the new ones. Keep a written prepared list in Notes or Personal Possessions if helpful.

Book entries also appear on the character sheet with casting buttons, even when they are not prepared. A casting button does not make an unprepared spell legal to cast. Use a registered spell only when prepared, or when casting an eligible Ritual from the book under this subclass’s rules. Registering a spell grants no extra slots or free castings. If the same spell appears through both Spellcasting and Spellbook, these are two entries for the same spell, not two separate castings.

Use the correct progression

Your effective Wizard level is one-third of your Fighter level, rounded down. D&D Beyond uses its native Fighter caster progression, which may show too many slots, a different preparation allowance, or different cantrip limits. Follow this table instead. Slot totals below are for this subclass alone.

Fighter level	Wizard level	Cantrips	Prepared spells	1st-level slots	2nd-level slots	3rd-level slots
3–5	1	3	4	2	0	0
6–8	2	3	5	3	0	0
9–11	3	3	6	4	2	0
12–14	4	4	7	4	3	0
15–17	5	4	9	4	3	2
18–20	6	4	10	4	3	3

Spells from a species, feat, or another class are tracked separately under the rules that grant them. For example, a level 10 Investigator records ten spells from level progression before any copied spells, knows three subclass cantrips, prepares six book spells, and has four level 1 slots and two level 2 slots.