Sekkar was distracted by his search for traps, but it did not mean he was not permanently on the highest alert. Pax might not realize herself yet, but her attention to the statue alone and then disappearance of Pensive combined with Kirin's shout pointed to the target. In one jump Sekkar was by the statue with Dawnbringer called out!

BA: activation of Dawnbringer

Attacks on the statue:

Attack: 19 Damage: 13  (in case of advantage for "Hold", second roll 26 )
Attack: 22 Damage: 10  (in case of advantage, second roll 20 )
Attack: 13 Damage: 14 + 6 (in case of advantage, second roll 17 )

Sneak attack: 17

Pax Init : 11

Initiative 11

Kaylyn, satisfied that there seemed to be no one in the room, followed the others inside.  As she did she would have cast Detect Magic, her action so natural to her that seeing magic was almost a primary sense of hers.  But she stood by the door while the others fanned out and searched.  She monitored Pensive as he flew about the room, his truesight a blessing that allows him see what cannot normally be seen.  But then he was suddenly gone, surprise and panic the last thing she feels from the small pseudodragon.

Statue WIS save: 19

Kirin feels the tingle on the back of his neck and whips around, firing off his spell almost instinctively. And yet the statue continues to move! Did his spell fail? Did the statue resist it?

These thoughts cross Kirin's mind as Dawnbringer blazes into view and in Sekkar's deft hands takes to the huge four-armed stone drow, scorching and splintering its surface with her light. (No advantage, but 54 damage!)

Rhayna is next

Kirin 23, Sekkar 22, Rhayna 21, Statue 15, Pax 11, Kaylyn 11

While examining the book, Rhayna is surprised by the statue, and summons two heavy tomes trying to clang the creature. (She casts Toll the Dead WIS Save DC 19 or take 25 necrotic damage.)

WIS save: 2 adv: 11

The two spectral books slam into the statue, and its surface begins to crack and pulverise, with small chunks and light dust falling to the floor. With a grinding noise the statue turns toward Sekkar and begins swinging all four of its large stone swords at him...

Attack: 13 Damage: 7
Attack: 24 Damage: 14
Attack: 16 Damage: 8
Attack: 18 Damage: 19

Now back to everyone! Pax and Kaylyn are next, followed by Kirin, Sekkar and Rhayna again

Pax considers her options for the briefest of moments, thinking about the racket this must likely be making, and decides to try and play for some time. She casts Otiluke’s Resilient Sphere at the creature.   (DC 17 Dex save or get caught in a force bubble.)

If it works, she says mentally, "It will only hold it for a minute. How can we quietly deal with this thing?" 

Sekkar was busy dodging the attacks, some of which still came through. (Using uncanny dodge to half the damage from attack 2)

"We can try to finish it off fast or figure out what was moved around in that corner," he nodded towards the spot where he saw the markings, "open thing up and get inside."

DEX save: 9

Pax's spell strikes the statue, and a large bubble begins to form around it... but then pops on the pointy ends of the four stone swords. The statue continues uninhibited...

Kaylyn's action is next

Kaylyn watched with sharp concern as the statue came to life and began attacking them.  Some sort of defensive measure she was sure, to protect the contents of the room.  She agreed with Sekkar, it must be stopped and quickly.  She pointed the rod she held in her one hand at the statue and 3 blasts of eldritch energy shot forth from her at the thing.

Attack: 32 Damage: 16

Attack: 27 Damage: Unable to parse dice roll.

Attack: 14 Damage: 16

"Temporarily solution as we are low on time and we must be quick," Kirin states as he points his staff at the statue, "Disappear from my sight," He cast Banishment on the it.

Cha Save 18  

(With a -5 CHA modifier, the roll is moot, but I'll roll it anyway...) CHA save: 14

Kaylyn's energy bolts blast more chunks off the statue, until Kirin's spell makes it suddenly vanish with a loud pop. A small patch of dust swirls in the place the statue was a moment earlier. A few papers blow off the desk onto the floor...

Kirin knows they have one minute until the spell expires and the statue returns.

(Out of combat for now, as long as Kirin's concentration lasts)

"We got a minute or until someone else requires my attention. What's this thing you need to open up?" When the thing is pointed out, Kirin will cast Knock on it to try and get it open. 

"No idea but it was over there," pointed Sekkar still standing on the "ready" for return of the statue.

Pax looks at the group, “Anyway for us to finish off this statue without making a big racket? Any place we can hide?  Or do we just tick the box away here, grab the book, and step outside?”

"I can only imagine that if that statue reappears and we are not here it will alert someone or look for us.  Unless it is somehow bound to this room, but we would have no way of knowing that."

She says this as she cross the room towards the spot where Pensive has disappeared.  She would still be concentrating on Detect Magic and examines the area where the marks on the floor are.  This would be the spot on the marble wall on the far side of the room, just to the right of the desk.  This area has the presence of magic.  She attempts to discern what type of magic may be on the wall.

Arcana 20

With the statue gone for now, Rhayna puts the book into her Haversack, so she can study it later. Being the librarian that she is. She leaves a note at the spot where the book is. "Borrowing this book. Will return. Promise. RN." Then she goes to inspect the wall were she detected magic.

Investigation (?): 29

(I am not sure if that's also where Kaylyn is also investigating.)

"If we're about to do what we're about to here in this city, he's not going to find that note or I doubt he'll be around for it to be returned to," Kirin comments as he look to see if his knock spell did anything.,

As Rhayna begins shoving a book into her bag Pax looks over at her. "Rhayna. Hey. What book is that? Don't just start shoving stuff into your bag. We're here looking for a book!  Is that the one?"