Superman (vol 2) #688 NM

THE FALL AND RISE OF JONATHAN KENT

While Superman has left Earth to take care of business on New Krypton, he leaves Mon-El in charge of protecting Metropolis whom has just abruptly discovered that his powers are gone, and he is plummeting to his death! He hits the drink, but is saved from drowning by the valorous Guardian – Mon-El's boss while he is in his secret identity of "Jonathan Kent", member of the Science Police.  Mon-El's powers, which seem to be cutting in and out intermittently, return just in time for the arrival of Squad K, a government team whose purpose is to "corral" Superman should the need arise. Ninety-eight seconds later, Mon-El has dispatched Squad K – their Kryptonite weapons ineffective against the Daxamite, proving he's not a Kryptonian. Mon-El and Guardian depart to visit Dr. Light, hoping that she can shed some "light" as to why Mon-El's powers are malfunctioning. She reveals that he is still suffering from lead poisoning. In fact, his superpowers are fighting of the potion that Superman gave him to nullify the lead-poisoning. Dr. Light estimates that he has a year to eighteen months to live. Mon-El takes the news rather well and asks Guardian to teach him how to fight so he won't be powerless when his powers fail – and how to swim! Mon-El then meets Mitch, the shop keep of the café below his home. Mitch tells him that "time rushes by before you know it."  Guardian, "Jonathan", and the Science Police break into a top-secret facility to rescue a friend, (some sort of DNAlien, Dubbilex, perhaps?). As they depart, Codename: Assassin stops them dead in their paths – but he lets them pass.