We analyze high signal-to-noise spectrophotometric observations acquired simultaneously with TWIN , a double-arm spectrograph , from 3400 to 10400 Å of three star-forming regions in the H ii galaxy SDSS J165712.75+321141.4 .
We have measured four line temperatures : T _ { e } ( [ O iii ] ) , T _ { e } ( [ S iii ] ) , T _ { e } ( [ O ii ] ) , and T _ { e } ( [ S ii ] ) , with high precision , rms errors of order 2 % , 5 % , 6 % and 6 % , respectively , for the brightest region , and slightly worse for the other two .
The temperature measurements allowed the direct derivation of ionic abundances of oxygen , sulphur , nitrogen , neon and argon .

We have computed CLOUDY tailor-made models which reproduce the O ^ { 2 + } measured thermal and ionic structures within the errors in the three knots , with deviations of only 0.1 dex in the case of O ^ { + } and S ^ { 2 + } ionic abundances .
In the case of the electron temperature and the ionic abundances of S ^ { + } /H ^ { + } , we find major discrepancies which could be consequence of the presence of colder diffuse gas .
The star formation history derived using STARLIGHT shows a similar age distribution of the ionizing population among the three star-forming regions .
This fact suggests a similar evolutionary history which is probably related to a process of interaction with a companion galaxy that triggered the star formation in the different regions almost at the same time .
The hardness of the radiation field mapped through the use of the softness parameter \eta is the same within the observational errors for all three regions , implying that the equivalent effective temperature of the radiation fields are very similar for all the studied regions of the galaxy , in spite of some small differences in the ionization state of different elements .

Regarding the kinematics of the galaxy , the gas rotation curve shows a deviation from the circular motion probably due either to an interaction process or related to an expanding bubble or shell of ionized gas approaching us .
A dynamical mass of 2.5 \times 10 ^ { 10 } { M _ { \odot } } is derived from the rotation curve .