Admittedly, I'd rather be obsessed with a masked blonde than a white whale or gaseous cloud, too.

From 1987, Tales of the Legion of Super-Heroes #346, reprinting 1986's Legion of Super-Heroes #21, "Obsession" Written by Paul Levitz, pencils by Greg LaRocque, inks by Larry Mahlstedt and Mike DeCarlo. 

The smartest Legionnaire was also often the most-tightly wound one, and Brainiac 5 is the obsessed one this issue, with trying to determine the secret identity of the mysterious, masked Sensor Girl. (A Legionnaire with a secret identity was unheard of; I can't think of another off the top of my head! At least, not one that maintained it for more than a brief story.) In a clandestine meeting near the earth's core in the middle of the night, Brainy brings his concerns to current team leader Element Lad, who still trusts Saturn Girl's recommendation of Sensor Girl. Brainy maintains they have to figure it out, but returns to headquarters with Element Lad; as they leave, alien Legionnaire Quislet arrives, snooping around for fun. (Quislet had been inducted the same time as SG...is this suspicious, or a red herring?)

Meanwhile, in space en route to a new prison planet after the destruction of Takron-Galtros, a Legion contingent attempts to put down a prison break of super-powered baddies like Titania, Sun Emperor, and the Fatal Five's Persuader. The breakout was engineered by another of the Five, the Emerald Empress, who is considering a new version of their team, and wondering if Persuader had been pulling his weight. Back on earth, Brainiac 5 uses his computer (or Computo) override to break into Sensor Girl's quarters, to find some clue: there was a hologram, but a hazy one that he couldn't make out; as well as her Legion flight ring! Then, how was she flying...? As in, flying into her quarters, pissed: she removes Brainy's senses, returning them after dumping him outside, then she arrives almost immediately thereafter to pitch in against the Empress. Sensor Girl is even able to stare down the Empress's Emerald Eye, and starts a grudge match with an backhand slap. With the Eye drained, the Empress settles for the tried-and-true Persuader, and leaves, to continue her recruiting drive another day.

As the Legion wraps up the other prisoners, Brainy leaps to a conclusion: Sensor Girl is really his lost love Supergirl, somehow still alive post-Crisis. Nope! It may not seem like a clue, but when Shrinking Violet asks Timber Wolf what he thinks, he's the closest: "Nobody could really do all those weird stunts." (Timber Wolf is my favorite Legionnaire, but he was not usually portrayed as the sharpest of the lot.) There is a fair-play answer, but you would have needed to have some history with the Legion; I don't think I had enough at the time, but still enjoyed the mystery.

Also this issue: "Training Session" Written by Paul Levitz, pencils by Paris Cullins, inks by Gary Martin. Wildfire tries to gauge the bizarre powers of Quislet; which is dumb, Quislet knows he's great! He--it?--also has a novel method of ditching Wildfire as well. Man, I wish we had gotten a little pack-in of him in the DC Universe Classics days; he was another favorite of mine.