Rewritten sentence: "Talking to them and telling them the truth is imperative."
The shift in mood is from a suggestion or recommendation to a command or instruction. The sentence can be rewritten as "Talk to them and you must tell them the truth."
The shift in mood occurs when the sentence goes from the imperative mood ("Talk to them") to the indicative mood ("you should tell them the truth"). To correct the sentence, it should be rewritten entirely in the indicative mood: "If you talk to them, it would be best to tell them the truth."
