Within the theoretical framework of nonlinear phonology, this paper proposes an account of tone sandhi and vowel deletion in Margi, a Chadic language spoken in Northern Nigeria. The database is Hoffman's Grammar of the Margi Language. Language-specific tonal processes in Margi are shown to originate in tone trapping, i.e., the impossibility for a tone to anchor to a skeletal slot by a universal mechanism. The paper identifies the circumstances leading to tone trapping (e.g., Vowel Elision) and formalizes the various tone-rescue processes available both word-internally and across words. Whereas trapped high tones are always saved (either taking over low-tone vowel positions or giving rise to contour tones), trapped low tones may remain trapp...