Dini, Kramer and Faucher give centre stage to the Riddler and Harley Quinn in Detective 837 (Dec. 2007), a tie-in to the Countdown weekly miniseries.
Edward Nigma’s agency is not doing as well as he had hoped, but things look to be turning around when Bruce Wayne comes to him with a case. One of his employees has gone missing, along with an experimental serum, and Bruce offers the Riddler a hefty sum to retrieve it, and find the woman.
The Riddler tracks her to Athena’s spa, a centre for the empowerment of women, which has become home to Harley Quinn, as seen in Countdown.
Harley relates the circumstances that saw her leave the Secret Six, something that occurred between their miniseries and ongoing book. Harley, along with Deadshot, Cat-Man, Scandal Savage, Knockout and Rag Doll, had been hired to protect an ambassador’s daughter during a parade. Instead, Harley and Rag Doll got into a fight, which distracted everyone enough for kidnappers to steal the girl. Harley got fired.
Holly Robinson, Catwoman’s sidekick, is also at the spa, as per Countdown, and joins the Riddler and Harley as they deal with the thief, who injects herself with the serum to take them down. It does not have the desired effect.
The Riddler retrieves the rest of the serum, returning it to Bruce Wayne. We learn that he hired the Riddler and paid him well, simply to keep him content as a detective, and less likely to return to crime.
The story ends as Athena turns over vial of the serum, extracted from the thief’s blood, to DeSaad.
Harley, Holly and Athena and her spa continue their storyline in Countdown.