The study reports the development of a continuously tunable excitation frequency-controlled cold atmospheric pressure plasma (CAP) device, its underlying physics and the associated unique discharge dynamics evolved under the variation of the external excitation frequency. The device is named as EFCAP to emphasise the ‘excitation frequency’ control aspect of the discharge. The absence of a dielectric barrier, very simple design, ability to operate with argon and ease of effective control via tuning of external driving frequency are some of the appealing features that drastically reduce device and operational cost. Significant controls achieved over dissipated power,discharge frequency, electron temperature, gas temperature and electronic excitation via tuning of frequencies are reported. While external excitation is in the kHz range, actual discharge dynamics were found to occur at a muchhigher frequency. Plasma–field interaction sets in complex interesting dynamics inside the torch, manifested in the form of spiral filaments and local hot spots. The evolution of the patterns by tuning the external excitation frequency is captured directly through fast photography and reported for the first time in CAP literature. The genesis of the patterns is examined from the synchronous time-domain behaviour of excitation pulse, discharge potential, discharge current and the corresponding frequency-domain behaviour.