Usando biblioteca assíncrona do caolan para node.js, eu tenho tentado chamar uma função que usaasync.series dentro de outra função que usa async.series, mas ainda não consigo executar as funções na ordem correta, conforme detalhado abaixo:

A saída do terminal mostra a segunda função sendo chamada antes da primeira, sem motivo aparente:

The "sys" module is now called "util". It should have a similar interface.
Starting the second step in the series
Value of b: undefined
Invoking the function firstStep
the value of toObtain is: [object Object]

E aqui está o código fonte correspondente:

var im = require('imagemagick');
var async = require('async');

var toObtain;


var b;
async.series([

function (callback) {
    //It appears that this function is being invoked after the second function.
    //Why is this happening?
    firstStep();
    callback();
},

function (callback) {
    //Why is the output of this function being displayed BEFORE the output of the function above? It's the opposite of the order in which I'm calling the functions.
    console.log("Starting the second step in the series");
    console.log("Value of b: " + b);
}]);


function firstStep(){
    async.series([

    function (next) { // step one - call the function that sets toObtain
        im.identify('kittens.png', function (err, features) {
            if (err) throw err;
            console.log("Invoking the function firstStep");
            toObtain = features;
            //console.log(toObtain);
            b = toObtain.height;
            next(); // invoke the callback provided by async
        });
    },

    function (next) { // step two - display it
        console.log('the value of toObtain is: %s',toObtain.toString());
    }]);
}