ðeɪ dɪskˈʌvɚ ðə dˈɑːktɚ sˈiːkɹᵻtli lˈɛft ɐ kˈoʊdᵻd mˈɛsɪdʒ wɪðˌɪn ðə ɹᵻkˈoːɹdɪŋ, ænd jˈuːs ɪt tə fˈaɪnd ɐ wˈɔːɹp sˈɪɡnɪtʃɚ ðæt ðeɪ kæn tɹˈeɪs.
They discover the Doctor secretly left a coded message within the recording, and use it to find a warp signature that they can trace.