In summaries, keep to one tense.
In summarizing the action of a drama, the writer should always use the present tense. In summarizing a poem, story, or novel, he should preferably use the present, though he may use the past if he prefers. If the summary is in the present tense, antecedent action should be expressed by the perfect; if in the past, by the past perfect.
An unforeseen chance prevents Friar John from delivering Friar Lawrence's letter to Romeo. Juliet, meanwhile, owing to her father's arbitrary change of the day set for her wedding, has been compelled to drink the potion on Tuesday night, with the result that Balthasar informs Romeo of her supposed death before Friar Lawrence learns of the nondelivery of the letter.