This novel details the origins of the Time Agents of the 51st century, first mentioned in the Fourth Doctor serial The Talons of Weng-Chiang.
ðɪs nˈɑːvəl diːtˈeɪlz ðɪ ˈɔːɹɪdʒˌɪnz ʌvðə tˈaɪm ˈeɪdʒənts ʌvðə fˈɪfti fˈɜːst sˈɛntʃɚɹi, fˈɜːst mˈɛnʃənd ɪnðə fˈoːɹθ dˈɑːktɚ sˈɪɹiəl ðə tˈælɑːnz ʌv wˈɛŋtʃjˈæŋ.