My protagonist Irene spies for the Invisible Library: a secretive inter-dimensional organisation. Its purpose is to acquire books (by any means...) from thousands of alternate worlds. And this helps supply balance to the multiverse. This also lets the Librarians pursue their private literary obsessions - but that's just icing on the cake.
The Library doesn't actually observe Christmas as a holiday. (In fact, they don't observe any specific holidays, and personal leave is handed out strictly at the discretion of a Librarian's own supervisor.) To the surprise of junior Librarians, giving and receiving Christmas presents between Librarians is tends to be discouraged. This often causes confusion. Surely giving presents is a sign of cooperation, of friendship, of sisterhood or brotherhood or whatever family relationship you like to idolise? How could this possibly go wrong?
The key point here is that these Librarians tend to be obsessive. They wouldn't spend their entire lives hunting books if they weren't. Experience has shown that finding the ideal present for another Librarian can be subverted all too easily. It can turn into a fervent and extremely dangerous hunt for a long-lost novel - possibly dragging along other Librarians and friends.
Even Librarians who couldn't care less about their colleagues can get drawn into extreme situations, just to prove that they can find a specific book when others fail to do so. Said book would then be handed over in a conveniently public place and in front of an audience, wrapped up with a bow on top, with a pleasant smile and happy Christmas wishes.
This story may be apocryphal, but it's still held up as a warning . . . It all started so innocently. Librarian A found out that her friend, Librarian B, had wanted The Confession of Father Brown for some time now. But this particular G K Chesterton edition could only be found in a specific alternate world. She resolved to surprise him with a copy of it for Christmas. She begged her supervisor for some personal leave, and went to the world in question - which happened to be in the middle of a raging war between a united fascist Europe and all the other world nations. Arriving in Oxford during an air-raid, she found herself having to penetrate the Bodleian Library. Challenging night-time roof-climbing was necessary, as was penetrating painted-shut skylights. The situation was further complicated by the fact that the place was being used as a secret testing site for training bats. They were being primed to attack enemy airplanes. When she finally escaped, book in hand, she could only hope that Librarian B would appreciate her hard work. It would be so depressing if he opened his present on Christmas morning, looked unimpressed, and then explained that he already had a copy. In better condition.
However, this isn't even as bad as the situation where a Librarian (Librarian C, to introduce another letter to the mix) delivers a present purely out of malice. The aim here is to give something which showcases the skill of Librarian C, and the lack of skill, or poor taste, of Librarian A. With dedication worthy of a much better cause, Librarian C will spend time and effort finding a copy of, for instance, an incredibly rare Sherlock Holmes variant. They will then hand it over on Christmas day with casual comments about how easy it was for them to find, and how they personally prefer more interesting books. Librarian A will have to sit there and take it with a smile. Outright rudeness would be unprofessional.
This sort of behaviour demands retaliation. Next Christmas, Librarian A will feel motivated to spend time and effort in making a similar gesture to Librarian C. As you can probably imagine, the situation escalates.
Senior Librarians have seen it all before, hundreds of times. It's easier just to avoid giving Christmas presents in the first place. Much less trouble in the long term.