ItreturnssixmonthsaftertheshockingfinaleofSeason3,andtheteammustovercometheirgrieftotackleadangerouscrimewave.Thistime,theglovesarewellandtrulyoffforProfessorTinhislecturesandanewmusicalpursuit,romanceisverymuchaliveforhismotherAdelaideTempest(DelaTour),andthelinesbetweenprofessionalandpersonalbecomeblurredfortherapistHelenaGoldberg(Stevenson).Meanwhile,DIMaiyaGoswami(SunetraSarker)takeschargeofthepoliceforcewithseriesfavoriteDSDanWinters(White)fiercelyatherside.
