Warning: Spoilers ahead. If you're not caught up on Arrow, don't read on.
Nicholas Lea, best known for his portrayal of Alex Krycek on the long-running FOX hit The X-Files, has inked a deal to play a recurring character in the second half of Arrow's second season. As an associate of Walter Steele, Lea's character--Mark Francis--is said to have a "huge role in changing the life of a Queen family member," and will appear in the just-wrapped episodes 12 and 13. Episodes 12 and 13, so it's been said, are titled "Tremors" and "Heir to the Demon." The second of the two features Nyssa al Ghul.
"Tremors," meanwhile, seems like it could be a reference to the earthquake machine that shook both Starling City and the Queen family to their respective foundations in the season one finale. There's some fallout from that undertaking yet to be dealt with, in the form of the revelation at the end of "State vs. Queen" that Thea Queen is, in fact, the daughter of Malcolm Merlyn. Merlyn, in "The Scientist," wanted Moira to reveal as much to Thea so that he could abscond with her but Moira's Hail Mary pass was to call Ra's al Ghul and inform him that Merlyn was still alive and in violation of his vow to the League. With Sara Lance and Nyssa al Ghul both appearing in "Heir to the Demon," it's probably safe to assume that the League of Assassins will play a significant role. What all of that has to do with Walter Steele, of course--well, there's the thing that's really hard to figure. Removing Steele and the potentially spoiler-saving name of "Mark Francis" from the equation altogether, my first guess would be Cain. David Cain is an assassin who's a generation older than Batman, Green Arrow and the other major heroes of the DC Universe. He's linked to the League of Assassins, extremely dangerous, and he's got a daughter who could be in the same peer group as Sara Lance and Nyssa al Ghul...named Cassandra. Bringing in David Cain at this juncture could tease not only Cassandra, but her mother--the master assassin known as Lady Shiva, one of Nanda Parbat's most feared killers and one of only a handful of characters whose voice wouldn't quiver at the name Ra's al Ghul. That could set us up nicely--either this season, or in the future--for either a showdown between Shiva and Ra's for control of the League or even just for someone to step in for Ra's if he's killed, arrested or otherwise removed from power this season. Cain is deeply entrenched in the culture of the League of Assassins, so there are really two ways that his involvement could play out that would radically impact the Queens. One of them seems more likely than the other, so we'll save it for second. Firstly, he could know somehow--perhaps via Ra's al Ghul, perhaps he can just tell by reading body language, whatever--that Thea is the daughter of Merlyn. He could spill it to her for one reason or another and set in motion the whole sequence of events that Moira has been terrified of ever since the revelation of her affair with Merlyn became known, and even moreso since Merlyn showed back up. A possible scenario that would have the added benefit of tying the character to Steele is that Steele did some due dilligence before marrying into the Queens and has known about Thea all along. If that's the case, any information at his disposal could come into the possession of an associate, and anyone working with the League of Assassins might see the value in Thea, since she's connected to both Merlyn and Sara, two of their "most wanted." The second, arguably more likely scenario (at least in that it opens up a whole new storyline instead of seemingly resolving a dangling one) is this: According to his Wikipedia entry, Cain is "one of the world's premier assassins, whose victims have included some of the most famous and powerful people on the planet." How could a man like that find himself an associate of the eminently decent Walter Steele? Well, he could kill him, of course. And since Steele has been instrumental to Walter and Moira keeping control of the company since Isabel Rochev's hostile takeover at the beginning of the season, losing Walter and potentially his investment could mean losing a grip on Queen Consolidated. At the very least, it could create some serious problems in the time before Moira gets whatever he may have left her in the will and is able to buy her way back in. Isabel might not strip the company for parts as quickly now as she'd hoped to at the start of the season--her relationship with Oliver has been evolving, after all--but operating at the level she does, you don't stay as successful for as long as she's supposed to have done by sitting on your hands when a limited window of opportunity opens.