jq: Cannot index array with string

Question

I have the following in a file (which I will call "myfile"):

[{
    "id": 123,
    "name": "John",
    "aux": [{
        "abc": "random",
        "def": "I want this"
    }],
    "blah": 23.11
}]

I could parse it if the file did not have the first [ and last ] as follows:

$ cat myfile | jq -r '.aux[] | .def'
I want this
$

but with the [ and ] I get:

$ cat myfile | jq -r '.aux[] | .def'
jq: error: Cannot index array with string

How can I deal with the [ and ] using jq? (I'm sure I could parse them off with a different tool but I want to learn correct usage of jq.