...is it possible? Or Does house Mercere's quaesitor have to be one of the (very few) gifted members.
Nothing says an unGifted Redcap can't be a Quaesitor. Obviously, he would be at a disadvantage when conducting investigations (as the Mercere chapted in HoH:TL points out) because of his lack of magic and, perhaps more importantly, magic resistance.
However, a few magical items can probably offset that. So I guess that House Guernicus, if given the choice between an undistiguished magical Mercere, and an unGifted Redcap with a strong reputation of intelligence, integrity, diligence and devotion to the Order would choose the latter.
I would guess there is exactly one, since Mercene does not have a lot of magi in the house, it is likely their one Quaesitor does not have the gift.
If you figure that a magi puts around 120 points into arts instead of skills and gets Hermetic Virtues rather that things like Keen Vision or Pussiant Folk Ken, a Quaesitor Redcap makes perfect sense.
My Verditius was considering trying to make silver rings which cast a touch range version of "Frosty Breath of the Spoken Lie" 50 times per day. Such a magic item would only be L26 , only around half the level of magic items a Redcap would get.
Unless your Tribunal has Peripheral Code prohibiting it, there doesn't seem to be any technical reason why not.
As far as I can see, the only problem is that a Redcap's lack of Magic Resistance means that his testimony/investigation is rather vulnerable to magical interference. Of course, that vulnerability might well be considered to be an advantage by the powerful members of the Tribunal.
You can always give the Redcap a relic to hold.
An outer tier member of Magvillus council by HoH:TL p. 44 needs to be a magus - and her judgement duties would also not sit well on an ungifted Redcap traditionally abstaining from voting at Tribunals.
A different question is, whether there are ungifted Redcaps among the Quaesitores in addition to the Magvillus council member from House Mercere. If they exist in a Tribunal, there would likely be some peripheral code sorting out and prioritizing their overlapping duties and responsibilities. I can imagine them best in the outer Tribunals (Novgorod, Levant, or such), where covenants are sparse and self-reliant, and most of their contacts with the remainder of the Order are through Redcaps.
Cheers
In an old sub rosa there was a quaesitor that was a shapeshifter. She used her animal senses to detect stuff and go to places where humans have difficulties fitting. So the investigation might be mundane, but it can be enhanced by supernatural means 
CHeers,
Xavi
I think you may actually be over-reading what's written. Here's the relevant passage (emphasis mine):
"The outer tier consists of a non-Guernicus Quaesitor from each of the other Houses and the Presiding Quaesitor from each regional Tribunal. A member of the inner council is usually the Presiding Quaesitor of the Rome Tribunal; the Primus only presides at the Grand Tribunal. Thus the outer tier consists of twenty-four magi. It should be noted that a number of the Presiding Quaesitors may well be non-Guernicus magi, but specific House representatives must still be nominated by the inner Council."
Remember that a Redcap has the same legal status of a magus. Considering the "thus", it then seems that in the passage "magus" is simply used as a shorthand for "member of the Order". Also, voting at the council is not the same as voting at Tribunals -- in fact, Quaesitors themselves abstain from voting at Tribunals!
Well, what you quoted is not the only statement on HoH:TL p. 44 referring to an all-magi Magvillus council - so interpreting the clear wording away would require some more gymnastics still. It would be pretty weird also, to have an ungifted Redcap - who does "not usually vote at Tribunal out of respect for true magi" (HoH:TL p. 82) - sit in judgement for all matters concerning the Quaesitores, that are not internal issues of House Guernicus only.
Cheers
The only other statement I find on p.44 is the one adding up all the numbers together (Primus, six inner council members, twenty-four outer council members): "The full council thus consists of thirty-one magi, including the Primus." This adds no information to the one I quoted above.
I do agree that interpreting away the clear wording, and over-reading the passage as a proof that the Gift is a requisite (and the second passage as further proof), requires a lot of mental gymnastics.
I don't see why it would be weird. It's clear that the purpose of having at least one represetative per house on the outer council is to guarantee representation, and the most representative member of house Mercere, given its function, is probably a redcap.
On the other hand, it would be very weird for a magical Mercere to accept a post on the outer council just because House Guernicus says "no unGifted rabble in our Council, please", given that magical Mercere "usually abstain [from voting at Tribunal] to avoid appearing superior to the Redcaps" (p.94).
Usually does not mean never. If a Mercere, either Gifted or unGifted, were made a Quaesitor I'm sure they would vote when they needed to vote. My guess is that it would be a Gifted one but it might be interesting to make a Redcap Quaesitor just to see what you could come up with. Mercere House might have lots of items for them to use since it would not be the first time.
Brother Cadfael anyone? Just with some supernatural virtues like second sight or the ability to detect traces of magic. Instead of the monk habit what protects him is the hat he wears 
Cheers,
Xavi
So two times the author clearly writes 'magi', and two times you say to him: "Well, you didn't mean 'magi'. You actually meant 'members of the Order of Hermes'." If that is fun, there is another three times at HoH:TL p.38. 
Representing House Mercere when judging the activities of the Quaesitores requires a very solid standing in the Order as well as in the House. After all, you might have to judge where a Tribunal has already failed, and in the council will always be the sole spokesperson of Mercere and its widespread interests: whatever the outcome, you have to broker it to your House-mates afterwards.
Cheers
Quite so.
That there are very good reasons for the representative of Mercere in the Magvillus council to be a magus does not mean, that IYC there can be no ungifted Redcap Quaesitores. I see many ideas in this thread how to make them interesting, useful and effective - and I made some experience with an ungifted Redcap playing detective myself.
Cheers
So your Guernicus council is all-male? The author clearly writes 'magi', and so you cant' be saying to him: "Well, you didn't mean 'magi'. You actually meant 'magi and magae'." Right? If that is fun, you are free to apply the same logic throughout the whole Ars Magica line. It's certainly a very original take on the game
However, you might also want to take a look at the rest of the Guernicus chapter -- for example all the rulings on the Code, where "magus" is almost invariably used to mean "member of the Order", regardless of gender or Gift.
I agree with you! Representing House Mercere on all its dealings with the Order requires a very solid standing in the Order as well as in the House. However, if such a standing were precluded to the unGifted, the Mercere Primus (or Prima, yes, let's be careful!) would never be unGifted.
::coughs:: Magi is the correct plural for a mixed sex group. Masculine takes precedence in this case, as it still does in modern Spanish, for instance, and formal, prescriptivist English.
More fundementally, unGifted Redcaps are Magi but they generally do not exercise their right to vote by tradition, not because they do not have said votes. Put in a situation whereby they are required to do so by office, and where they do not vote except in cases where said office is important, I cannot see anyone except someone engaged in no correspondence complaining.
Right, I absolutely agree. Unless one is specifically and explicitly making a distinction between magus and non-magus members, one should assume "magus" means any member of the order, male or female, from "full" Hermetic magi to unGifted Redcaps to hedge wizards ex Miscellanea.
Note that discussions and votes on the Guernicus outer council are not Tribunal votes. They are discussions on how the Code should be applied and interpreted. House Guernicus explicitly included representatives of the other Houses so that all to whom the law applied could have a voice in it. It seems in some sense even more natural for an unGifted Redcap to represent his house, because a) the house is mostly unGifted, b) he'd be the only representation for unGifted members of the Order, and c) unGifted Mercere tend to be more familiar with Redcap duties, and there's a lot of Code that specifically applies to Redcaps.
Ah, many dispute this assertion in the name of political correctness. I'm not one of them, though!
However, using masculine alone for a mixed gender group (instead of stating " and ") goes hand-in-hand with using masculine for an individual of unknown gender (instead of stating "a or "). Someone really nitpicky could argue that since Ars magica sometimes uses "maga" instead of "magus" even when the gender is unknown, then a writer who wanted to refer to a mixed gender group would use "magi and magae", and so by usage of "magi" alone implies an all-male group.
Is this reasonable? Not at all; in fact, it was used as an example of how over-reading a simple passage can bring one to completely illogical conclusions.
In the Hermetic Oath (ArM5 p. 13) you will usually find 'member of the Order of Hermes' and 'sodalis/sodales'. There are two exceptions, namely "... Wizards' War is an open conflict between two magi who may slay each other without breaking this oath, ..." and "No apprentice shall be called a magus until he first swears to uphold this code." In both cases the use of 'magus' instead of "member of the Order" makes sense: an ungifted Redcap cannot participate in Wizards' War, and "No apprentice shall be called a member of the Order of Hermes until he first swears to uphold this code." would be a meaningless tautology.
Of course I don't have the time to analyze "the rest of the Guernicus chapter -- for example all the rulings on the Code" for examples of unprecise wording. So you have to look for your fun there alone.
Insatella is by far more clever than you make her: "She does not have the Gift and is very withdrawn; she tries not to involve herself in the affairs of magi or the politics of the tribunal, but instead concentrates on seeing that her House and the covenant run as smoothly as possible." (HoH:TL p. 79)
Cheers
This is canonically false, or at least potentially false of the story/legend is true
Redcaps of the Order are magi and magae of the Order, with all the rights and privileges thereto.
Magus is a rank and a social status, not a career. Redcaps are magi (check out the House Mercere section of the Core rules if you don't believe me), they just happen to be unGifted Magi. Apprentices are not members of the order; they are the property of members of the order. Killing an apprentice is an attack against his parens, and regarded as depriving someone of magical power rather than assault. Spell casters who are not members of the Order are not, by the Order's view, Magi but merely magic users. Calling such a one magus would be flattery, not truth, in the mouth and eyes of an Hermetic diplomat. In short, Magus does mean "member of the Order"; they are synonyms.
Redcaps are like the British royals: They have lots of rights and, of their own free will, refuse to use them because that would cause problems. Nevertheless, they do still possess said rights by law.
ETA: quoted badly, fixed it.