“Hi servi invivi quos quaeris non sunt.”*

At one point in Parlor Games I needed someone to speak an incantation to get rid of an unwelcome guest, and as everyone knows, the appropriate language for issuing either Priestly or Arcane orders is, appropriately, a Dead Language. Unfortunately, my parents persuaded me to take French instead of Latin in high school (I now think we were both mistaken and I should have studied Spanish, instead). Luckily for me, however, one of the lovely women in my writer's group is apparently quite proficient in Latin. I didn't realize to what degree until I asked her to translate this line for me:

Locate the intruder, follow him to his abode. Let not darkness nor mysteries cloud his flight. Show him to me.

Today I got back the most giggle-inducing post. I can't help it; I love linguistics. If I were incurably rich I'd do nothing but study languages all day. When I wasn't writing or practicing tai chi, of course. Below are the most relevant portions of the text Alysen sent me (the comments in italics are mine):

Ave salveque Holly!

A. Nouns

invasor = invader
speculator = spy, scout
emissarius = emissary, spy

Oddly enough, there’s no single Latin word which means, precisely, intruder. There are a couple of awkward two- and three-word phrases which I dismissed, not wanting to open up the grammatical and metrical cans of worms they entailed.

Is the intruder intruding on his own recognizance? Invasor. Or has he been sent as a minion by a nefarious secret master? Emissarius or speculator.

domicilium = abode, dwelling-place
domus = home, house
latibulum = hiding-place, retreat, subterfuge
latebra = hiding-place, den, lair

Domicilium is colorsell and metrically annoying. Domum, in addition to being the generic term for house, home, household, also refers to a specific type of building, an atrium townhouse, and carries a connotation of middle-class comfort--hardly what you had in mind.

Latibulum is okay, but I hope you like latebra, lair, as much as I do. (oh, yes!)

obscuritas = darkness, meanness, obscurity (by an amazing coincidence)
opacittas = darkness, shadiness, opacity (another amazing coincidence)
arcanum = mystery, secret
occultum = hidden thing, secret (adj. used as substantive)
tenebrae = darkness, obscurity, night, mysteries (I thought of you, Joy!)

Why not let tenebrae suffice alone, since it means both darkness and mysteries?

fuga = flight, fleeing, exile
effugium = flight, way of escape

Either is fine, leaving meter the only criterion.

B. Verbs

invenio, invenire = invent, contrive, find, discover, procure
rescisco, resciscere = ascertain, find out, learn
reperio, reperire = find, meet with, find out, descover, invent

I recommend reperio, reperire; it seems closest to your intended meaning. Oddly, again, there seems to be no single Latin word meaning precisely “locate”, “find the location of”.

It would be a clause like “locum invasoris rescisce”, ascertain the place of.

sequor, sequi = follow, go after, attend, pursue
investigo, investigare = track
venor, venari = hunt

Which of these you choose depends on whether the counterintelligence agent being ordered on this spychase is singular or plural. Solo minion or squad? I’ll get to the reason in a moment.

sino, sinere = allow, permit
patior, pati (?) = bear, undergo, suffer, allow
permitto, permittere = let go through, let fly, give up, entrust, allow, permit (am. coinc.)

This one’s complicated by the fact that the negative imperative (your “Let not”) is conveyed by noli / nolite plus the infinitive, literally meaning “Do not will to [verb].” So there are going to be two infinitives in this sentence, potentially confusing but unavoidable.

nubibus velo, velare = envelop, veil, conceal by/within clouds; becloud
caligine velo, velare = ditto by mist
nebula (long A) velo, velare = ditto by fog

I’d recommend caligus, fog, if you insist on atmospheric phenomena; but velo, velare conveys your meaning without assistance.

retego, retegere = uncover, bare, open, reveal
recludo, recludere = open, disclose, reveal
revelo, revelare = unveil, bare, show, discover
patefacio, patefacere = disclose, expose, bring to light

Here again the choice depends on whether you’re sending a single operator or a team on this mission.

C. Esthetics

Any magical incantation ought to have some poesy about it. Lain poetry doesn’t have to rhyme--although it often does, almost inadvertently, due to the inherent structure of the language--but rhyme and rhythm must inevitably improve the potency of any magic spell! ;-)

Aha, you say. Comes the dawn.

Commanding a Single Minion:

Invasorem reperi.
Eum ad latebram [suam] venare.
Tenebras effugium [suum] velare
caligine noli sinere.
Eum mihi retege.

Literally:
Invader discover.
Him to lair [his] hunt.
Darkness/mysteries flight [his] to veil
by mist do not let.
Him to me reveal.

(The suums/suams are metrically annoying and can be deleted, taken as
understood.)

I am confident that either of the above, chanted sonorously, will suffice to send any spook skeddadlin’ with its ectoplasmic tail between its legs.

Vale!

*(These are not the droids you’re looking for.)