What happens in Canto XXIII of Dante's Inferno?

Canto XXIII
Dante and Virgil have stolen away after the Malebranche become distracted by attacking sinners in the boiling Phlegethon of Pouch Five.
Soon they observe sinners in a grim procession. They walk single file; Dante compares their steps to those of the “Minor Friars.” He is referring to the Franciscan monks who walk in this manner; additionally, the hypocrites doomed for eternity to this pouch of Hell are dressed in monkish garb.
As they proceed, Dante recalls a story about a frog and a mouse written by Aesop, the ancient Greek fabulist. In this tale, a mouse asks a frog to carry it across a stream. The frog agrees, but when the pair has traveled about halfway across, the frog goes underwater. The mouse drowns but its body floats to the surface. A hawk (also known as a “kite”) flying overhead spies the both the frog and the mouse, swoops down and eats them both.

“Silent, alone, and without company
We went, the one in front, the other after,
As go the Minor Friars along their way.
Upon the fable of Aesop was directed
My thought, by reason of the present quarrel,
Where he has spoken of the frog and mouse;
For 'mo' and 'issa' are not more alike
Than this one is to that, if well we couple
End and beginning with a steadfast mind.”

Dante is fearful that the demons from which they took their leave will be angry at their unannounced departure and will pursue them. The very thought is terrifying and makes Dante’s hair stand up. He says to Virgil:

"These on our account
Are laughed to scorn, with injury and scoff
So great, that much I think it must annoy them.
If anger be engrafted on ill-will,
They will come after us more merciless
Than dog upon the leveret which he seizes,"
I felt my hair stand all on end already
With terror, and stood backwardly intent,
When said I: "Master, if thou hidest not
Thyself and me forthwith, of Malebranche
I am in dread; we have them now behind us;
I so imagine them, I already feel them."

Virgil does not comfort his protege; instead, he agrees that the demons will be furious and suggests they hasten their departure, deeper into Pouch Six.
Both of the travelers are correct; their fear is justified. Just as soon as Virgil recommends their hasty departure, the angry, winged demons appear on the horizon. Like a mother who will protect her child at all costs, Virgil swoops Dante into his arms and spirits him away as quickly as possible. When they come to the edge of a precipice, Virgil sits and they slide down together. The travel downward reminds Dante of water flowing over a mill; while swift, they feel every bump along the way:

"When I beheld them come with outstretched wings,
Not far remote, with will to seize upon us.
My Leader on a sudden seized me up,
Even as a mother who by noise is wakened,
And close beside her sees the enkindled flames,
Who takes her son, and flies, and does not stop,
Having more care of him than of herself,
So that she clothes her only with a shift;
And downward from the top of the hard bank
Supine he gave him to the pendent rock,
That one side of the other Bolgia walls.
Ne'er ran so swiftly water through a sluice
To turn the wheel of any land-built mill,
When nearest to the paddles it approaches,
As did my Master down along that border,
Bearing me with him on his breast away,
As his own son, and not as a companion."

They finally reach the bottom, much to Virgil’s relief as the demons may not pursue them into the next pouch. This greatly enrages the Malebranche, who howl in fury as they watch their prey get away unscatched:

“Hardly the bed of the ravine below
His feet had reached, ere they had reached the hill
Right over us; but he was not afraid;
For the high Providence, which had ordained
To place them ministers of the fifth moat,
The power of thence departing took from all.”

Now safely in Pouch Six, the pair can observe the denizens. Here, men in golden cloaks walk as if they can barely move. Outwardly, they are dazzling but inwardly they are miserable. These sinners move exceedingly slowly, crying as they go, and weighed down by the lead that lines their garments. This punishment mimics the execution technique of Frederick II, who killed those condemned by placing them in a leaden enclosure which then was fired until it melted around them:

"A painted people there below we found,
Who went about with footsteps very slow,
Weeping and in their semblance tired and vanquished.
They had on mantles with the hoods low down
Before their eyes, and fashioned of the cut
That in Cologne they for the monks are made.
Without, they gilded are so that it dazzles;
But inwardly all leaden and so heavy
That Frederick used to put them on of straw.
O everlastingly fatiguing mantle!”

Dante asks Virgil to help him identify anyone he might know. Before Virgil can respond, one of the shades overhears Dante’s accent and cries out for the travelers to stop. The poets tarry and two of the sinners approach, looking them over wordlessly:

“And one, who understood the Tuscan speech,
Cried to us from behind: "Stay ye your feet,
Ye, who so run athwart the dusky air!
Perhaps thou'lt have from me what thou demandest."
"Whereat the Leader turned him, and said: "Wait,
And then according to his pace proceed."
I stopped, and two beheld I show great haste
Of spirit, in their faces, to be with me;
But the burden and the narrow way delayed them.
When they came up, long with an eye askance
They scanned me without uttering a word.”

The shades confer among themselves, asking each other whether or not Dante is a living soul. They also want to know why the travelers are not dressed in the golden, leaden robes:

“Then to each other turned, and said together:
"He by the action of his throat seems living;
And if they dead are, by what privilege
Go they uncovered by the heavy stole?"
Then said to me: "Tuscan, who to the college
Of miserable hypocrites art come,
Do not disdain to tell us who thou art."

Dante wants to know what causes the shades to cry so much. They explain that the robes are made of lead and unbearably heavy. They are being punished in this manner because they are the “Jovial Friars.” This was the nickname by which the military order called the “Glorious Virgin Mary” was known. The order, “Frait Gaudenti,” gained a wide reputation as being unobservant of their vows. Addtionally, they failed to keep the peace and the region of Florence known as “Gardingo” became particularly violent and corrupt. Catalano and Longeringo are two of that order, and they are the ones who come to speak to Dante and Virgil:

"These orange cloaks
Are made of lead so heavy, that the weights
Cause in this way their balances to creak.
Frati Gaudenti were we, and Bolognese;
I Catalano, and he Loderingo
Named, and together taken by thy city,
As the wont is to take one man alone,
For maintenance of its peace; and we were such
That still it is apparent round Gardingo."

Dante becomes distracted from the Jovial Friars’ tale when he sees an enormous man, naked and pinned to the ground, in the pose of one who has been crucified. This, Catalano informs Dante, is Caiaphas, the man who ordered Jesus crucified alone instead of all the Jews. In this undignified and painful manner, Caiaphas must pass eternity; additionally, for all time as well, anyone who crosses through Pouch Six, steps on and over him. Moreover, Catalano continues, the same fate has befallen all of Caiaphas’ relatives and friends:

“This transfixed one, whom thou seest,
Counselled the Pharisees that it was meet
To put one man to torture for the people.
Crosswise and naked is he on the path,
As thou perceivest; and he needs must feel,
Whoever passes, first how much he weighs;
And in like mode his father-in-law is punished
Within this moat, and the others of the council,
Which for the Jews was a malignant seed."

Virgil is horrified at the sight and wants to depart. He asks the Jovial Friars if exiting is possible without tipping off the Malebranche. Catalano replies that there is a bridge that the travelers may cross; although it is broken in many places, enough of the rubble protrudes to make passage possible. Virgil is irritated that the demons have lied to him; his surprise is curious to Catalano, who responds that lying is the nature of devils and they should not be trusted to tell the truth:

"Many of the Devil's vices
Once heard I at Bologna, and among them,
That he's a liar and the father of lies.”

Still annoyed, Virgil takes his leave and Dante follows obediently after him.