Complex sentence: Hearing the phone ring inside, Doyle rushes to let himself into his apartment, but a menacing Caliph demon--hired to strong-arm Doyle into paying a debt--greets him from the shadows.
Split into simpler sentences: Hearing the phone ring inside, Doyle rushes to let himself into his apartment. Just as he's about to answer, a menacing Caliph demon--hired to strong-arm Doyle into paying a debt--greets him from the shadows.