Is the expression "the dead of night" or "the dead of the night"?

The second article of in the dead of the night doesn’t sound so good to my modern ear. I would strongly advise skipping it and leaving just in the dead of night.

At most!

Why at most? Because — as it turns out — you don’t even need that first article, either. You can just write in dead of night and be done with it, just as Shakespeare did. For example, from Shakespeare’s long poem, The Rape of Lucrece:

Imagine her as one in dead of night
From forth dull sleep by dreadful fancy waking,
That thinks she hath beheld some ghastly sprite,
Whose grim aspect sets every joint a-shaking;
What terror ’tis! but she, in worser taking,
From sleep disturbed, heedfully doth view
The sight which makes supposed terror true.

Or here again in verse, from the Dryden translation of Virgil’s Æneid:

At length, in dead of night, the ghost appears
Of her unhappy lord: the specter stares,
And, with erected eyes, his bloody bosom bares

The OED

The OED defines dead of night as follows, and gives these citations, some of which have a the and some of which do not:

dead of night, of winter: the time of intensest stillness, darkness, cold, etc.; = ‘depth’ (of winter)

• 1548 Hall Chron. 109 b, — In the dedde of the night..he brake up his campe and fled.
• 1583 Stanyhurst Æneis iv. (Arb.) 113 — Neere toe dead of midnight yt drew.
• 1601 Shaks. Twel. N. i. v. 290 — Euen in the dead of night.
• 1613 Sherley Trav. Persia 4 — My iourney was under-taken in the dead of winter.
• 1793 Smeaton Edystone L. §266 — At dead of neap, when the tides run less rapid.
• 1807-8 W. Irving Salmag. xx. (1860) 452 — In the dead of winter, when nature is without charm.
• 1840 Macaulay Clive (1867) 25 — At dead of night, Clive marched out of the fort.

If it were me, I would just say at/by/in dead of night, without any other adornment.

Prosaically Put

For those who would like Modern English prose examples instead of poetry, here are some quotes from George Martin’s Game of Thrones:

• They consorted with giants and ghouls, stole girl children in the dead of night, and drank blood from polished horns.
• He had been born in the dead of winter, a terrible cruel one that the maesters said had lasted near three years, but Tyrion’s earliest memories were of spring.

As you see, Martin always uses in the dead of night/winter. That’s probably the most common form.

Here, however, are some from J.R.R. Tolkien, who is generous enough to provide us with all three variants:

• He found he could hide from daylight and moonshine, and make his way swiftly and softly by dead of night with his pale cold eyes, and catch small frightened or unwary things.
• In the dead of the night many shining eyes were seen peering over the brow of the hill.
• To that Stone the Company came and halted in the dead of night.
• ‘We saw it also, but that was in the dead of night before Gandalf left us.’

I believe that shows that all three can have their use in just the right place.

Google Books

And for those who want Contemporary English prose examples of the version without any articles at all, here are some random excerpt taken from Google Books:

• A man on a "bed of terror" lulls himself with the vivid chronicle of a journey perhaps never taken, when a solitary cyclist rolled down an eerie street, reading a newspaper in dead of night. Ubiquitous bicycles glisten in the mind, in the reader's ...
• And, if they were fleeing by dead of night, at least they were running toward help, and not into greater danger.
• And why came that old farmer from the woods at dead of night, stealing toward the Wissahikon, with his four tall sons around him, armed with rifle and with knife?
• Asia described the frenzied manhunters: “It was like the days of the Bastille in France. Arrests were made suddenly and in dead of night......Detectives, women and men, decoys, and all that vile rabble of human bloodhounds infested the city.
• At least one keg of gunpowder was missing from the powder cave. Zanja waited there until a summer downpour had lightened to a mist, then she traveled east in dead of night and slipped into the river valley under cover of darkness.
• ... beds vacated by adolescent males yearning for women, rising in dead of night, tiptoeing in fear of the slightest resonance of chattering bones, tomblike silence, barely disturbed by complicit barking, serving as go-between in lovers' intrigues.
• By dead of night, maybe that same night Jaruel had come to see his older brother , Nahum's bags were packed and his brother took him to the docks in Boothbay. If there wasn't a ship moored there that was hiring on, they would spend the ...
• he assembled his three hundred Spartans, put himself at their bead, marched through the defile, in dead of night, and, with sword in hand, rushed like a torrent upon the Persian camp, overturning all in his course, until he had nearly reached
• He himself is always in the pure cool mountain air and beholds the sun when all below is still engulfed in dead of night. But there is more than a pull toward the heights motivating Schopenhauer; there are pushes from below. Two other traits ...
• He seemed to see such cars everywhere. Driving past the man's house, he wondered whether he might be able to steal back in dead of night and destroy the car, dismantling the wiring, and then make it back to his own house undetected.
• in a modern drawing room in Bengal, in a journey during which both mythic and ordinary place-names are made strange: For thousands of years I roamed the paths of this earth, From waters round Ceylon in dead of night to Malayan seas.
• In dead of night, which is that moment between unwinding and winding, your life comes up, waits for you. It says, it is over, it is over, it is over. What have I done, what have I not done, over, over the night breathes, it is over. Someone you have
• I should sneak into a barracks at an unguarded moment or in dead of night and loot someone's footlocker for a pair of leather gloves. Next I'll have to remove a gas mask that hangs on a peg over somebody's bunk and hang it over mine.
• Margaret did not know he was at home: had he stolen like a thief by dead of night into his own dwelling? Depressed as Jem had often and long seen him, this night there was something different about him still; beaten down by some inward ...
• My homeland, I cannot bear to think of you in dead of night. Lustrous stones are rooted there still while my sap's gone dry. You ask, my friend, How deep this grief? Simply a spring swelled river too eager to ...
• Not alone the dead, but the living likewise, are given to be burned in secret here ; and into this canal, at dead of night, are flung the rash wretches who have madly dared to oppose with speech or act the powers that rule in Siam. None but the ...
• Now, in dead of night, I wake again and again to the screen door caterwauling its accusing silence. That cat's a conjunction cut from my poem in one fell swoop of your pen, it's gone, but it's left a trail of blood on the unprotected page and I can ...
• on the other side of the earth's globe, communities thrived under the warmth of an afternoon sun. The moon, she wrote, was, for the first time, a visible token, shining in dead of night, that the sun was still blazing somewhere, in an August sky.
• Others, like David Carriere of Ottawa (geocaching handle “Zartimus”) go caching only by dead of night. “It was the only time I could find to go,with the kids and all,” he tells me, but I'm not entirely convinced by his innocent explanation. Zartimus ...
• So, accompanied by the Pope's own envoys, a party set forth by dead of night but had no sooner opened the tomb than they were interrupted by revellers returning fromone of the patriotic banquets whichhad becomeso popular in recent ...
• That Worth did not hesitate to plunge into a churning river at dead of night, clad in prison clothes and aware that apprehension might well mean death, reflected both his physical toughness and a growing faith in his own invincibility.
• The Abbey was torn down by Henry VIII, in a fervour of asset-stripping, and the stone parcelled out to nobles in London to build their fine houses. But a lot was stolen in dead of night, and many old houses in these parts have chunks of Abbey ...
• The man who had stood high on the armoured car in dead of night had not been a lone wolf; he was part of a pack that would get noisier and stronger. Bolshevism was finding its confidence again. A leader had returned to Petrograd who ...
• Then, on by deluxe personnel carrier in dead of night to Best Eastern Hyangsan Hotel in Myohyang for a refreshing debriefing in the internment spa. Your final day in the DPRK is awash in the sights and sounds of Panmunjom in the heart of ...
• with a product of the Office of Strategic Services, the legend-making OSS, whose operatives were expected to parachute into enemy territory, slit the throats of sentries in dead of night, and pass pouches of golden sovereigns to bearded men

The phrase in the dead of night is idiomatic for late at night, or in the stillest part of a night. While the variation “the dead of the night” is not grammatically wrong, the excrescent the is a bother and a possible source of ambiguity. For example, one might refer to the people that died in a given night as the dead of that night.