ondertussen means “meanwhile”. When it opens the clause, the verb comes before the subject (inversion).
Connective adverbs · Bijwoorden
Zij kookt. Ondertussen dek ik de tafel.
She cooks. Meanwhile I set the table.
Wacht even; ondertussen zoek ik het op.
Wait a moment; meanwhile I'll look it up.
Drag scrambled words into the right Dutch order and master inversion and the verb-final rule.