Amazingly enough, Lost's first 2005 episode (which at the time of its original broadcast marked a return on TV after a four-week break) feels like a so-called "filler", i.e. something that is put together in the most basic way while the better stuff is waiting behind the corner. Of course, in the case of Lost, even a filler episode is above average, since the show's mythology is consistently present in the shape of the Island.
Picking up some time after the previous episode, Whatever the Case May Be starts with Kate and Sawyer finding a suitcase while swimming. Kate knows what's inside and wants it, but Sawyer refuses to had it over, resulting in a conflict that eventually calls for Jack's help. Meanwhile, Shannon wonders what Boone and Locke are doing in the jungle every day, but soon has other things on her mind when Sayid asks her to help him translate some notes he got from Rousseau. As for Charlie, still sad because of what happened to Claire (well, that and almost dying), he gets some healthy advice from Rose (L. Scott Caldwell), no stranger to matters of the heart since her husband Bernard, who was on the plane with her, hasn't turned up yet.
As for the suitcase, hints to what it may contain are given in the Kate-centric flashbacks: while applying for a bank loan using an alias (the usual Maggie or Meg), she finds herself right in the middle of a robbery, with her own life on the line. Or not, as it turns out: the robbery was her idea all along, so that she could access a safety deposit box, numbered 815...
Aside from that final coincidence, which is never directly addressed, this is very much a character-based episode, with no real focus on the ongoing mysteries and more scenes featuring various interactions. Some of these (Kate and Sawyer) are fun but very basic, some (Sayid and Shannon) bordering on trivial, but there's real emotion in Charlie's conversation with Rose, and there's that Locke/Boone subplot which promises a good payoff. Plus, there's one revelation about Kate that is guaranteed to have long-term repercussions. In other words: textbook Lost, albeit a bit lightweight.