Anybody who's seen their share of sci-fi knows that scientists are big fans of uploading their consciousness onto computers. With a thorough scan of his own brain, a mad genius can use the data to create a simulated version of himself, which is usually intended to make his knowledge and expertise available after his death via the spiffy/creepy interface of his own voice and personality. In some cases, this act prompts very little reaction from others, aside from some clunky exposition to explain the deus ex machina of him being there and a general appreciation for his helpful pointers (see: Superman's hologram dad in Man of Steel; the pilot for Jem and the Holograms). But in other cases, the mere idea that a person's inner self can be replicated via a machine freaks everyone out, and poses terrifying questions related to the existence of the soul and the ultimate meaning of the human experience (see: Transcendence).
The scientist who embarks on the ill-advised adventure in this instance is Dr. Will Caster (Johnny Depp), whom we first see giving a sort of TED Talk about his work with artificial intelligence. He explains, with guileless optimism, how he just can't wait for that moment when computers become self-aware -- a concept often called the "technological singularity," which you may remember from the Terminator and Matrix franchises as the reason for the apocalypse.
But Will isn't worried; he thinks that humans will evolve to accommodate this leap and usher in a new era of human/machine consciousness. He gets to test this theory almost immediately after the talk, when an antitechnology activist shoots him with some kind of isotope-laced bullet (?) that will slowly kill him over the course of about a month. That's just enough time for Will's wife and partner in AI research Evelyn (Rebecca Hall) to upload every detail of his brain onto a computer system, including, with any luck, his every memory and thought. The hope is that Will's conscious life will continue even after his body dies, and he and Evelyn won't have to bear the pain of separation. And it works! Sort of.
Evelyn's happy about virtual Will, but everybody else is terrified. After all, he's effectively achieved the "singularity" he was talking about, and with the entire Internet at his disposal, he can exist in any computer in the world, earn Evelyn a bazillion dollars on the stock market, and help her set up a giant lab in Nevada to carry out their vision for that new era he was talking about right before he got shot. The CIA is worried that the power they're amassing with Will's limitless capabilities isn't safe for the rest of the world, and there's some underlying creepiness about whether virtual Will should be trusted.
There's doubt from the word "go" as to whether the entity that first speaks to Evelyn through the terminal is really Will, and this should be no surprise, because fiction has been grappling with what exactly constitutes the "self" for ages. We wonder: Is a copy of Will still Will? If Will has a soul, does it reside in his uploaded consciousness? Or has his soul moved on to some afterlife? And in that case, what does that make virtual Will?
In a weird way, these themes play out across most genres, not just Asimovian sci-fi. Films about zombies are more or less always wrestling with the fear that there's some ephemeral component to the human experience, and that if you lost it, you'd become something horrifying at the bottom of the uncanny valley, alive in all ways except the one that makes you who you are. In zombie movies, that turns you into animated meat. In science fiction, you become a freaky, disembodied voice.
All of this thematic stuff is worth noting, because Transcendence is otherwise very straightforward. There's no Matrix-sequels abstract weirdness or Kubrickian symbolism; it's just a totally literal narrative. That opens the film up to some problems: Namely, the fact that when you ask a deep question in the text (as opposed to the subtext), you have to answer it in the text, and it's hard to do that without sounding stupid. However, the movie is far from a vapid attempt to cover complex ideas solely through stunts and explosions (see: I, Robot), or a psychodrama that only uses science-fiction ideas to serve a personal premise (see: Her). In a way, the relatively balanced approach that Transcendence takes to its subject matter is the most interesting thing about it.