Savannah is the kind of girl who doesn’t swear, doesn’t drink and doesn’t lie. During her spring break, she helps build houses for charity and her dream is to open a summer camp where special needs children can play with horses. Her ideal first date is eating at a local diner (“I don’t want to go somewhere nice, I want to go somewhere good”) and then connecting with her date’s autistic father for an hour.

John is the kind of guy who has a quick temper, but a kind heart. He used to be tough (he has scars from a knife fight!) and emotionally restrained, but he’s trying to change and open up. He’s selfless and chooses to re-enlist in the army after 9/11, even though all he wants is to be with Savannah, because it’s the right thing to do.

“Dear John” is the kind of movie where people like Savannah and John actually exist. But, more importantly, thanks to the performances, “Dear John” is the kind of movie where you’re willing to believe people like Savannah and John could actually exist.

Channing Tatum and Amanda Seyfried play their roles so earnestly and authentically that the film simply clicks emotionally. For fans of Seyfried, this is no surprise: at the age of 24, her career has already displayed the range of actresses twice her age. After getting her start as a “plastic” in “Mean Girls,” Amanda has played everything from the confident lead in the musical “Mamma Mia” to the heart-breaking daughter in HBO’s “Big Love” to a nerdy high schooler in the horror film “Jennifer’s Body” to a sexy seductress in this year’s indie “Chloe.” To Savannah, she brings wide-eyed naiveté and unparalleled sincerity. Seyfried maintains a slight daze in her eyes, a mysterious element that allures us, but we can’t quite get past.

It is Tatum’s performance, rather, which is revelatory. For an actor best known for his abs and his work in “She’s the Man,” “Step Up 2: The City Streets” and “G.I. Joe,” the likelihood Tatum could hold his ground opposite Seyfried seemed unlikely. But “Dear John” is Tatum’s movie through and through — we follow his story throughout and only see Savannah through his eyes. Tatum handles both brooding military sequences and tear-jerking emotional moments in stride. When Tatum reads a letter he wrote to his father, it’s easy to forget that this was the guy overshadowed by Amanda Bynes in drag in “She’s the Man.”

The film itself is quite firmly set in its genre of “Nicholas Sparks Novels.” For those who have seen “The Notebook” and “A Walk to Remember,” “Dear John” is much of the same. The plot twists work better in “Dear John” than in most of Sparks’s films: two twists, in particular, knock your socks off. Visually, the movie is gorgeous, set in a lush Charlestown backdrop.

But, in the end, “Dear John” isn’t so much about plot or cinematography, it’s about chilling with Savannah and John for two hours and taking it all in. It’s a small film, but it’s simply immersive.