Note: This is another in my sequence of post-Mystery-Hunt cryptics, which started with "Still There," "Post-Game Predictions," "The Sequel," "Power Lines," "A Lesson in Cryptography," "Yet More Villainy," "Further Escapades," "Time X*X," "Honeymoon in Segas," "If At First You Succeed," "Another One From The Vault," "Next Winter: Wonderland," "DAB," "Some Extraction on the Side," "Another Campaign," "Mind The Sharp Bits!", "Through The Wood," and "Newbie Toonie"; this one was written before the 2023 hunt and refers to the 2021 and 2022 hunts. "NI2" and "NI3," as is usual in the National Puzzlers' League, indicate the second and third editions (respectively) of Merriam-Webster's New International Dictionary.

After all this time, the Professor here at MIT has reestablished communication with ⟂IW; alas, things have gotten rather messy over there:

Stellar Creatures. In December 2021, creatures from outer space started appearing on ⟂IW campus. These were not rats; the differences between universes result in differences in living organisms, including:

• Microinversions: One character is replaced by another character or vice versa; these two characters (always the same two) are exact opposites in a way that is often (but not always) sex-related.
• Macroinversions: Everything but the head is inverted.

The Examination and the Monarchy. Unexpectedly, the attempt to deal with these creatures in ⟂IW's 2022 Hunt was not successful, and they are still at large. Fifteen clues have an extra letter at the left or right end of a word, which must be deleted before solving; examine these letters in clue order to see why the attempt has not yet succeeded. Fortunately, teams have just gained access to a realm called Tomezone, whose library-focused leadership (the Monarchy) can offer an alternative perspective. Specifically, four of the (post-deletion) clues are ambiguous, each having an alternative, too-short answer of 1–3 letters (all different), which is the result of removing 1–4 letters (all identical) from the end of the real answer; one letter in the too-short answer will be the same as the "curtailed" letter(s). Put two circles next to each of the fifteen clues, and where the extra letter in the clue word was on its left or right, mark the left or right circle (respectively); then for each ambiguous clue, if it yields n "curtailed" letters, move its mark n circles downwards. The result (appropriately read) will say where things went wrong, and also (split into two pieces) will name your contact at the Monarchy.

Pair-Around. In eleven "pair-filled" grid squares, the Across and Down answers have different letters (put both in the grid square). From the center of each such square, you can draw a line (length ≤ 4) to the center of another square so that all these lines form a single, symmetrical path running through all the pair-filled squares and ending with a non-pair-filled square. Taking the pair-filled squares in path order:

• The letters from the Down answers will give an unhelpful description of the entity causing the problem.
• The letters from the Across answers will name the department in the Monarchy that can handle the entity.
• Where a given pair-filled square holds the pth letter of the Down answer and the qth letter of the Across answer, the pth word of the Down clue and the qth word of the Across clue will have, in one position, the same letter; these letters (still in path order) will say where this entity can be safely put.

The Terminal Part. To complete the cleanup process, the agents of the above department must make a journey. In each of the eight clues not used above, the wordplay yields a letter sequence with one or two (identical) extra "directional" letters (N, S, E, or W); draw a line in the grid starting at the center of the letter before the extra letter(s), in the direction indicated by the extra letter(s), whose length is twice the number of extra letters. These lines, which will form multiple paths, will say (in lowercase letters) what mode of transport will be used. The place they are going is themed around a certain kind of tome, appropriate to the ongoing delays that have occurred; to find out what kind, you can (depending on your preferred language) either:

• Read the starting letters of the lines in the paths, along each path, path by path; or
• Put the path from the Pair-Around and all these paths into your Monarchy contact's first name.

ACROSS

1. Brown soda water from Vichy in your mouth (5)
6. Fig bush parts that wheelwrights ring with spokes (4)
9. Friendly game involving cards and images, chiefly (4)
12. Cervine swallows Georgia's small vapor-removal device (8) [NI2]
13. Well, Juliet finally runs up against Romeo (4)
16. Part of nastier wine-growing region (4)
18. A shoemaker's "sample" solution to | 3 – ln x | = 2 (5)
19. Varied every other letter of synonym Owens used (2-4)
20. Second barrier with 50% kaolin backing cardboardlike materials (7) [NI3]
21. Have actress Vivien on the dais alone (4)
22. I deny that Charlie turned blue hand green (4)
24. Figure from Egyptian myth is cloned (4)
26. Hindi part of sign next to Vigoda's 'hood (4)
29. Benatar flipped over one Tiberian appetizer (4)
30. Bridge bid from Yoko that keeps Lena loss-free (3 2)
32 & 34. [See instructions]
35. Trio of ornithologists enters station? Not exactly (5)
36. Chicken claiming Mr. Weasley is a non-chicken (4)
37. Some beef astounds a bridge player (4)
38. Omani coin-tossing results in retreat (4)
39. Test — or, initially, assess — eland (4)
41. Gp. gutted anadromous salmon (4, abbr.)
44. More insightful wrapper's our team coach (7)
47. Tomb beside old seed container (6)
50. Ecstatic echidna's head is clearing (5)
51. Who's left on earth that reflects sufficiently poetically? (4)
52. Tailor's wife flees soothsayer (4)
53. Lawyer's on the threshold of unraveling mini-line (2 6)
54. Thus, Ulee's debut ought to be a bit of singing (4)
55. In speech, convince folks to buy phone (4)
56. Badger takes trees (5)

DOWN

1. Drive twice a year when an operation gets launched (1-3)
2. Boom! Rio now includes a bunch of stars (5)
3. Cold, alien, semi-yellow type of alcohol with 16 carbons (5)
4. Posse after aging frontier leader in One Word With Bucco (4)
5. Viper confused cute, boring tool about which verbs are perfect or imperfect, say (9)
6. Hide from hammy Dr. Frankenstein's third monster (5)
7. Was originally near a beast one might be riding around, obstructing a waxer (5 2)
8. Runner uttered word preceding "-Ball" in an arcade (4) [NI3]
10. Earp misinterpreted a measurement of a plot (4)
11. Attorney General Ed displays more than one elk, humorously? (5)
14. Again assemble rare shell of emu egg? Excellent (7)
15. Saskatchewan city controller getting back in box inside of islands (6)
17. Pass up stuffing containing no alcohol, and red-and-yellow Sapindus fruit (9)
21. Some places that house outspoken office-holders (4)
23. Like the systems we use to classify ailments Congo's oil cured (9)
25. Herb is wise (4)
27. Carry indigo Italian port (4)
28. Press out the right bits of the flag plant Mr. Wu considered hale (7)
31. Broadcast Dotty, not Victor (2 2, abbr.)
32. Cooks like to feed children (6)
33. Darn author mentioned pair of swords once used instead of bootlace (4 3) [NI2]
38. Flags festooning Armory's highest stories (5)
40. Portion out everything bots unwrapped (5)
42. Short one thanks Christmasy character (5)
43. Smell strongly of sulfur, tin, and potassium (5)
45. Dog story hits your ear (4)
46. True example of an aquatic bird! (4)
48. Phrase connoting exotism captioned pic possibly found with a Google search (4)
49. Must pay (and secondarily console) Anderson who made Fantastic Mr. Fog (4)