How to add data to an array (MongoDB) from Socket.IO? (node.js)

I've got the following MongoDB Schema's

//MongoDB Schema    

var Line = new Schema({
    id    : Number,
    user  : String,
    text  : String,
});


var Story = new Schema ({
    sid: {type: String, unique: true, required: true},
    maxlines: {type: Number, default: 10}, // Max number of lines per user
    title: {type: String, default: 'Select here to set a title'},
    lines: [Line],
});

For a particular story the data in MogoDB looks like this:

{
__v: 0,
_id: ObjectId("5084559945a0a23c1b000002"),
lines: [{
        "id": 1,
        "user": "Joe",
        "text": "This is line number 1"
    },
    {
        "id": 2,
        "user": "Adam",
        "text": "This is line number 2"
    },
    {
        "id": 3,
        "user": "John",
        "text": "This is line number 3"
    },
],
maxlines: 10,
sid: "lJOezsysf",
title: "A New Story!"
}

I'm using Socket.Io to communicate with the server and push the messages to other users

// when the client emits 'sendline', this listens and executes
    socket.on('sendline', function (data) {
        // we tell the client to execute 'updatestory' with 2 parameters
        io.sockets.in(socket.room).emit('updatestory', socket.username, data);  
        Story.findOne({ sid: socket.room }, function(err, story){

           **    What would go here to update MongoDB? **

            console.log(socket.room);
        });
    });

How can i use the above to add the data from socket.io and save it to MogoDB?

socket.room has the same value as sid on Mongo so it finds the correct entry.
socket.username = user
data = text

I've tried to use the below, to save the data but i get an error, i want it to create a new entry in the 'Line' array with the next id.

Story.Lines.User = socket.username;
Story.Lines.text = data;
Story.save();

What method would i use to push this to the db?

* EDIT *

Managed to get it to work, seems like i was using Story rather than story.

Code i used below:

    Story.findOne({ sid: socket.room }, function(err, story){   
    story.lines.push({ 
    user: socket.username, 
    text: data,
     });