Cannot assign value of type '(String) -> Page' to type 'Page'

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if segue.identifier == "startAdventure" {
            if let pageController = segue.destinationViewController as? PageController {
                pageController.page = Adventure.story
            }
        }
    }

class Page {
    let story: Story

    typealias Choice = (title: String, page: Page)

    var firstChoice: Choice?
    var secondChoice: Choice?

    init(story: Story) {
        self.story = story
    }
}

extension Page {
    func addChoice (title: String, story: Story) -> Page {
        let page = Page(story: story)
        return addChoice(title, page: page)
    }

    func addChoice (title: String, page: Page) -> Page {
        switch (firstChoice, secondChoice) {
            case (.Some, .Some) : break
            case (.None, .None), (.None, .Some) :
                firstChoice = (title, page)
            case (.Some, .None) :
                secondChoice = (title, page)
        }
        return page
    }
}

struct Adventure {
    static func story(name: String) -> Page { //Static readonly computed property prevents against story being changed
        let returnTrip = Page(story: .ReturnTrip)
        let touchdown = returnTrip.addChoice("Stop and Investigate", story: .TouchDown)
        let homeward = returnTrip.addChoice("Continue Home to Earth", story: .Homeward)
        let rover = touchdown.addChoice("Explore the Rover", story: .Rover)
        let crate = touchdown.addChoice("Open the Crate", story: .Crate)

        homeward.addChoice("Head back to Mars", page: touchdown)
        let home = homeward.addChoice("Continue Home to Earth", story: .Home)

        let cave = rover.addChoice("Explore the Coordinates", story: .Cave)
        rover.addChoice("Return to Earth", page: home)

        cave.addChoice("Continue towards faint light", story: .Droid)
        cave.addChoice("Refill the ship and explore the rover", page: rover)

        crate.addChoice("Explore the Rover", page: rover)
        crate.addChoice("Use the key", story: .Monster)

        return returnTrip
    }
}