The Legion of Super-Heroes is finally returning to mainstream DC continuity. To celebrate the return of the 30th century’s most powerful teenagers, hop in the Wayback Machine for a tale DC probably would just as soon like to forget.

“Secret Origins,” you may recall, was DC’s go-to title for the untold tales of the roots of DC’s cavalcade of champions. Apparently, when you run out of heroes, you create an all-headquarters issue, because there’s nothing more exciting than drywall, construction dust and the smell of sweet, sweet blueprints.

Mmm … blueprints …

“Secret Origins” No. 46, cover date December 1989, throws open the doors on the Justice League cave, the Titans Tower and the Legion of Super-Heroes clubhouse.

For those wondering, Grant Morrison penned the Justice League tale, and it’s so not ending up in any Morrison omnibus any time soon. But we’re here to focus on the Legion story, and it’s a doozy, even for a team with a pet monkey wearing a cape.

Now I always considered the Legion clubhouse to be the answer to Doctor Who’s Tardis – a minor exterior with an almost infinitely large interior. From many of the old “Adventure” comics, it looks like an inverted rocket about 15 feet high – yet it’s capable of housing two dozen teenagers, laboratories, armories, brigs, recreation rooms, space vehicles, time cubes and more.

Wasn’t it always just there?

Yet in “The Little Clubhouse That Could,” written by Gerard Jones, also listed here as Word Boy, and illustrated by Curt Swan, Pencil Lad, and Ty Templeton, Ink Lad, the three founding members of the Legion, Saturn Girl, Cosmic Boy and Lightning Lad, are in a jam.

In this tale set shortly after they met, they’re desperate for a meeting space. They’ve already advertised for superhero tryouts so they can add to their numbers.

Frustrated, they just take over the nearby public park. First up: Arm-Fall-Off-Boy, who can detach his limbs and use them as weapons.

As opposed to all the other heroes who use their non-detachable limbs as weapons.

And Arm-Fall-Off-Boy becomes the first, in this continuity, anyway, of a joke who can’t believe he was rejected.

Next up: The arrogant Mnemonic Kid, who can blast people into short-term memory loss – and if she keeps zapping them, she can turn them into mental infants.

Alas, she can’t restore those memories, proving her code name to be a lie, as she shows when she hits a toddler and makes him forget his address.

Our goodniks hate her attitude and send her packing.

“Oh yeah? You’ll regret this, creeps!” she vows.

Something tells me we haven’t seen the last of Mnemonic Kid.

And you have to wonder why these teen heroes never bothered to vet applicants before having them show up on their doorstep – or public grass.

Before we start singing the praises of bureaucracy, the top contender is up next: Fortress Lad!

Fortress Lad, I must note, is such a significant creation, that he gets his own credit at the top of the story, attributed to DC Editor KC Carlson.

Looking like a cross between a clown and a walking Hazmat suit, Fortress Lad reveals his secret origin – dun-dun-dun!

His home planet, Fwang – yes, Fwang – suffers from constant barrages of meteors.

He explains, “…. all Fwangian boys, at puberty, gain the power to become metallic fortresses for the protection of others.”

There’s a joke about teenage boys and boners in here somewhere, but we have to keep moving.

The trio reject Fortress Lad.

“We don’t see how your power would be of much use to superheroes like us,” Lightning Lad says.

Suddenly Mnemonic Kid attacks!

She blanks the memories of our heroes, and as she prepares to finish them off with a laserlike weapon, Fortress Lad dashes forward and becomes hard – well, erect – OK, metallic – and absorbs our three amnesiac teens.

Mnemonic Lad retaliates by blasting the galaxy’s No. 1 Fwangian hero repeatedly, to destroy his memory. She regresses him to less than a baby.

The delay, however, allows the Legionnaires to regain their senses, more or less. They slip out his front door – can someone let Charles Darwin know evolution is more like an episode of “This Old House”? – and confront the Kid.

She tosses a grenade, but Cosmic Boy halts it with his powers. It explodes, killing our one-shot villain.

The three heroes are then left with one burning question: Where did this clubhouse come from?

“That must be part of our memory forever destroyed by Mnemonic Kid!” Lightning Lad says.

“But I have an odd feeling of ….fondness … for this building, almost as though it were a person,” Cosmic Boy adds.

Sure, a person whose dreams you crushed just a few minutes ago.

But our cheery omniscient narrator tries to tack on a happy ending of sorts.

“And so, Fortress Lad got to join the Legion after  all – although no one ever knew it … because Fortress Lad himself was left with only a single thought …”

“… Never give up … Never give up … Never give up.”

You mean to say the all-powerful Saturn Girl, the super-smart Brainiac 5 and the dreamy Dream Girl never got a clue that their residence was actually a sentient lifeform? A being trapped in the shape of a building, unable to resume his normal form, forced to endure the habits of two dozen alien teenagers living inside him?

Can you even imagine how Timber Wolf tears into the boys’ bathroom after Taco Tuesday?

What the sprock did this poor kid do to deserve that hell? And why did we have to know it?

Some origins are better left secrets.