“What do you see, Wyattson?” 

“The emanations suggest a spell of the sixth circle, and the glimmering resonance is the celestial signature of the Silver Flame. There’s only one woman in Sharn who wields the Flame with such power—Ythana Morr.”

“Well reasoned, my friend, but look more closely. That celestial resonance that drew your attention is merely sprinkled atop the true signature of the spell. I don’t recognize the energy… but it has the stink of Mabar about it.” 

I’ve just published an in-depth look at House Medani, one of the main sources of inquisitives in Eberron, so I’ve been thinking about how I like to run mysteries and investigation campaigns. Magic is a part of everyday life in Eberron; it’s a tool people use in place of the technology we use in our world. There are countless ways spells can be used to commit a crime—but how can an Inquisitive investigate this? I love the image of a detective using Detect Magic to pick up details of the crime, like someone in our world would evaluate ballistics or DNA. However, by default, Detect Magic only provides details of the school of magic associated with an effect. I like to go deeper. If an adventurer who’s proficient in both Arcana and Investigation and who’s capable of casting Detect Magic studies a scene, I will give them the opportunity to find traces of spells that have been used in the recent past, potentially gaining any of the following details… typically in this order. 

• Traces. How many spells have been used in the area that’s being studied in the last 24 hours? This is the first step; the investigator might have a vague sense of relative power and time. If they pick a spell to study, they have an opportunity to obtain additional information. 
• School of Magic. This is the easy default; Detect Magic allows anyone to do this, with no proficiency or check. 
• When was the spell cast? This will be approximate, but it’s something. 
• What level spell slot was used to cast the spell? This is a basic mechanical element of spells and in my opinion, it’s a concept people understand within the world itself; it’s a basic measure of the power of a spell. I generally prefer to use “circle” instead of “level” just because I prefer the sound of it. But I’ll allow an expert to recognize the level of a spell effect. 
• What is the Power Source of the spell? Broadly, what type of magic is it? Arcane? Divine? Primal? Generally, I will allow a professional who’s able to cast Detect Magic to make this determination without being familiar with the magic in question; you don’t have to be a cleric to identify divine magic. However, if the spell is something more exotic, I might limit things; psionic spells or something associated with an exotic warlock might show up as “an unknown form of energy manipulation”—unless the investigator has prior experience with that form of magic. 
• Spell Signature. Once the investigator has identified the power source of a spell, they may be able to glean more specific details about the spell or the spellcaster. For a Divine spell, the basic signature reveals the faith of the spellcaster: Sovereign Host, Path of Light, Silver Flame. With a Primal spell it will reveal the druidic sect or tradition. For an Arcane spell, it reveals the literal school where the caster learned magic; Arcanix has an entirely different style from the war magic of Rekkenmark, the workhorse training of the Twelve, or the esoteric precision of Aereni magic. If the user is self trained, that will be evident; “It’s an unconventional, haphazard style, probably self-taught.” If the DM doesn’t know these specific details, it might provide a broad sense of nationality of the caster; we’ve never named any schools of magic in the Mror Holds, but Mror arcane spells have a signature that’s broadly different from those of Breland or Aundair. When appropriate, the DM can also say that the investigator identifies the distinctive style but doesn’t recognize it—this would be appropriate for the magic of Argonnessen, the Lords of Dust, or a unique Cult of the Dragon Below. The point is that once they’ve encountered in once, they’ll recognize it when they encounter it again. 
• Further Details. The power source and signature provide a solid foundation: It’s a divine spell associated with the Blood of Vol or it’s an arcane spell cast by someone trained at Rekkenmark. But an exceptional investigator could potentially pick up additional information. A simple discovery would be information about the components used in the spell: did they use sulfur to cast this Fireball or did they use a pinch of refined dragonshard? Were they rushed—casting in the middle of a fight—or did they take their time? What sort of arcane focus did they use—a rod or a wand?

So, how much of this information can a specific adventurer get about a particular spell? My first question is How much information do they NEED to progress the story? A basic rule I live by is never ask a player to roll a die if I’m not prepared for every possible outcome. If the adventurer is a professional inquisitive trained in Arcana and Investigation, it may be that they just get the information if they choose to look at it; it’s their specialty. Or it may be that I ask them to make an Intelligence (Investigation) check, but they’ll always learn that the spell was divine magic cast six hours ago; it’s just that if they get at least 15 they’ll also learn that it was a Seeker of the Divinity Within and if they get 20 or higher they’ll know it used a 5th level spell slot. 

On the other hand, if it’s a totally random search and failure is on the table, I might use a formula like this: 

Investigation—Arcane Forensics. Spend ten minutes studying the area; this includes casting Detect Magic as a ritual. This provides a sense of spell effects that have been used in the area within the last 24 hours and the schools of magic involved. To study a specific spell, make an Intelligence (Investigation) check. The base difficulty is 10, increased by 3 for every six hours that have passed since the spell was cast. If the check is successful, the caster can learn one detail: time of casting, power source, or spell level. For every 3 points above the required difficulty, they can learn one additional detail. Once the power source has been identified, this can include the signature and further details. 

Another example of using Investigation in conjunction with a spell to gain more detailed results would be Locate Animals and Plants, which I could see as a light version of looking for traces of DNA. Once again, I might just let the Inquisitive with the spell get basic information without a roll. But if I asked for a roll, it would be something like this…

Investigation—Traces of Life. Spend ten minutes studying the area; this includes casting Locate Animals and Plants as a ritual. This provides a vague sense of the types of creatures that have been present in the area over the last day.  To study a specific spell, make an Intelligence (Investigation) check. The base difficulty is 10, increased by 3 for every six hours that have passed since the creature was present. If the check is successful, the investigator knows the species of the creature. For every 3 points of success, they can learn an additional detail chosen by the DM. This could be age, hair color, whether they were injured, something about their clothing; whatever could be reasonably deduced. So with a result of 22 they could learn There was an old male dwarf who was wearing heavy armor.   

Right away, these two options highlight a difference between the Medani inquisitive—who can innately cast Detect Magic—and the Tharashk inquisitive, who can Locate Animals and Plants. Medani gets more information about the mystery, while Tharashk excels at finding people! Of course, there’s other skills that can help an investigation without the use of magic. By the rules as written, Medicine allows someone to “determine what killed the recently slain.” Based on the results of the check, this could be as simple as the types of damage they suffered in their final moments (“acid damage”) to a more detailed analysis (“a massive gout of acid that struck them with significant force—perhaps the breath of a dragon.”) Survival allows someone to “follow tracks,” but I’ll also let them use Survival to reconstruct a scene—ranging from “You can tell there were three different humanoids here” to “They entered together, there was a struggle, and the smallest of the three was dragged out.” In both these cases, anyone could make a check to get the basic information, but I’d limit the more advanced details to a character who’s proficient in the skill. A d20 roll is a wild spectrum, and in my campaign I like to give a little weight to Proficiency; it’s not just that you get a bonus to the role, it’s a skill that’s important to you and that you’ve invested time in. 

Of course, there’s a secondary aspect to this: The ability of a master criminal to cover their tracks. Starting with skill alone, Deception is the key. If someone if proficient with Deception and with the skill associated with their style of magic (Arcana for Arcane, Religion for Divine, Nature for Primal) I’ll allow them to attempt to disguise their spellcasting. This works much like using Deception against Insight in a conversation; I’ll have the schemer make a Deception check using their spellcasting ability score, and describe the false signature they are trying to create. With skill alone, I wouldn’t allow this to change Power Type or School; but they could alter the signature, trying to make their Karrnathi Seeker spell feel like a Brelish Vassal spell. Note the Deception score and compare any subsequent Investigation to that score; if the Investigation check is lower, they will be fooled. For someone trying to stage a scene or hide cause of death, I’d likewise require proficiency in both Deception and the relevant skill (Medicine, Survival). Depending on nature of the scene or the injury, true deception might be impossible; it’s hard to make someone who’s been burnt to death appear to have been killed by slashing damage. On the other hand, I’d likely allow the deceiver to try to conceal the actual cause of death—IE, if someone was killed by having their throat cut and the deceiver bashes their skull in with a mace, it’s easy to determine that the creature suffered both slashing and bludgeoning damage; it will take an excellent check to determine which injury was post-mortem. For this sort of use of Deception, I’d personally use an Intelligence (Deception) check.

Since blocking divination tends to be higher than accessing them, what kinds of magical countermeasures could lower casters take to mask their signatures or otherwise throw off the scent of a Wolf?

Mechanically, the core of this is Deception, as described above. The point is that you can do lots of things—cast your Fireball using guano instead of sulfur, using a staff instead of a wand, and so on; but we need a mechanical measure to tell whether the Inquisitive is able to see through your ruse, and that’s where we employ the test of Deception vs Investigation. That’s where we get You can see that they tried to emulate the Aundairian style by using a wand, but the Rekkenmark training is still clear in the scent of the ashes. A commenter suggests the use of unusual components, such as Mabaran crystals, and I think that’s an excellent option; that’s the sort of thing where I’d a) allow someone to make a Deception check even if they don’t have the appropriate proficiencies or b) give someone with appropriate proficiencies advantage on their Deception check. But the point is that the expert investigator should always have a chance to see through the ruse; if there’s a foolproof way to fool even the greatest inquisitive, there’s not much point to telling stories of investigations!

I will say that we haven’t done much discussion on TOOLS that help people get away with murder. An assassin may not have the ability to cast Nondetection or Pass Without Trace, but they could have an amulet that erases their aura to Locate Animals (although in this case, the expert inquisitive might notice the absence of an aura; they can’t get specifics, but they can tell magic was employed to conceal it). Likewise, there definitely should be a “Wand of Silence” that allows someone to drop verbal components when using it as a focus to cast evocation spells. But that’s a concept to explore in another article…

Anyhow, these are house rules I use in my campaign; they may or may not be right for yours! Thanks as always to my Patreon supporters, who make articles like this possible. And since I’ve got Medani on the mind, here’s a bonus: a Medani focus item that amplifies the divinatory powers of the Mark of Detection!