  We present results of a multi-year study of the high-amplitude $\delta$ Scuti
(HADS) star GSC 03144-595. The star was observed between June and September in
2011 and 2014 for 13 nights and 28 nights respectively. Based on our results we
argue that GSC 03144-595 is a new triple-mode radially pulsating HADS, only the
fifth discovered and only the second that has a fundamental frequency in the
traditional $\delta$ Scuti regime. While the frequencies and amplitudes of the
fundamental and first harmonic were found to be unchanged between 2011 and
2014, we found that the amplitude of the second harmonic increased by 44\%, a
form of evolution not previously seen. This finding suggests that the second
harmonic may be transient, thus explaining the scarcity of triple mode HADS
stars.
