play along

Short definition from Wiktionary

Verb

1. 1
   To take part in a charade, deception, or practical joke.
2. 2
   To participate in a joke or trick while hiding one's knowledge of its true nature.
3. 3
   To play a musical instrument in synchrony with a playback of a recording.
4. 4
   To cooperate or go along with a plan.
5. 5
   To pretend to cooperate or go along with a plan.
6. 6
   To manipulate (someone).
7. 7
   Used other than figuratively or idiomatically: see play, along.